Maintaining Johnson 9.9 TroubleshootingJohnson, Evinrude, OMC, outboard motor, outboard motor repair, outboard troubleshooting, 9.9, 15 hp, year of manufacture, water pump, carburetor, long shaft, 15 hp conversion, sailmaster


Troubleshooting Johnson/Evinrude 2 cycle Outboards Under 20 HP

(Engine Troubleshooting)   



I have had a lot of pleas from frustrated boaters, saying that their problem is not discussed on any of my articles.  Well, they usually are, however maybe I describe what I cover in slightly different terms than they are used to.  And if they do contact me for help they do not indicate anything that has already been done to the motor.  I give my thoughts and possibly their somewhat sarcastic reply is that has already been done numerous times (if I recommend cleaning the carb, which IS NOT just spraying cleaner in the airbox).  Maybe I have not made it very clear that I FLUNKED MINDREADING SCHOOL years ago.


With troubleshooting, NOTHING is in black and white, kind of like going to the doctor, you need to explain your situation in terms that HE can use, (not just that I feel bad) and let the doctor do his/her diagnosis.  This may even require a follow up to verify or require more tests.  We all have to go by what we have learned (either book learned or seat of the pants type).  And for outboard motor related situations, sometimes initially it is hard to separate out electrical from fuel related issues.  Then at times it may even be operator error.


In this article you may see a bit of duplication, and as mentioned above, this may be to give a partly different perspective on the same issue.  The symptoms may be slightly different, but the cures could be the same.  I also make additions to these articles over time and may make duplications as it is hard to re-read the whole article to find a section where I may have covered a bit differently before, so this is the case, here I ask for forgiveness.


Water is the Number One Essential For an Outboard Motor to Function ;  These articles constantly expose me to many pleas for assistance by e-mail.  Here is a somewhat typical request for assistance.

I read your article on maintaining my 1972 Evinrude 6hp.   However I have a problem that you do not seem to cover.   I ran the engine recently and no water came from the exhaust port while in my yard or in the water.   I also took the engine cover off and the engine block was smoking it was so hot, clearly not receiving cooling water.   I figured it was the impeller because it was an old engine.  


To give you further information as to the repairs i've done:  I bought a new impeller from West Marine, which is the exact impeller that it was supposed to replace.   I cleaned the impeller plate, and the plate below that (where the water first comes in from the intake) and tried to clean the housing to make sure there was no free debris inside of it.   I installed a new impeller as you described in your article and it simply does not work.  It pushes a very small amount of water with the engine in neutral and while its in gear...   I just don't understand why it doesn't work.   I also checked the thermostat (there was no thermostat, and one of the cooling passages was clogged) which I unclogged and poured boiling water down all the other passages to ensure there was no clog anywhere in the cooling system.   If you have any suggestions for why it is not working I would greatly appreciate them, and the location of a rebuild kit that works (the one with the stainless steel housing inside of the OEM housing) would also be greatly appreciated if you feel it is necessary.   Thanks so much, I really do appreciate your page and advice.


My Response ;;;


 I guess the 1st thing I would do is check the water intake screen in the housing behind the prop to see if it allows water flow in.  And on that motor, the water intake is directly behind the prop, which needs to have the motor in forward gear to force water into the screen & up into the water pump.


 2nd would to pull the thermostat cover & start it up to see if any water is getting beyond the water pump.  You might also consider installing the Pee tube that I mention in the article instead of relying on the blubber hole on the rear of the exhaust housing.


 3rd  Pull the head & check for any obstructions in the water jacket & under the headgasket.  Also check in the water jackets along the cylinder walls to block.  


 4th do you have the grommet in properly & not folded over on the top of the water pump outlet to the tube??


 5th   There has to be a grommet of some sort on the top of the water tube from the water pump at the juncture of the block.  However I cannot find any in the illustrations.  I don’t remember if I have ever had these powerheads off the exhaust housing, so cannot be sure what it is, but I know on the 9.9 & 15s from 1972-1992 those grommets can deteriorate & swell up over time, blocking water flow into the block.


As for a different water pump, this motor does not need a lot of cooling water as compared to the larger motors, so unless your water pump housing is really damaged, I do not see any need to replace it, the bottom wear plate maybe, if it is scored.


I am not a mechanic & my shade tree’s leaves are falling off rapidly at age 81, and I therefore do not have access to a lot of info other than seat of my own pants.  Again try an old  Evinrude dealer, or some mechanic that makes his living working on motors, not the internet video jockies.   West Marine may be OK for impellers, but I doubt if they know anything beyond what the book or computer says.


Again I would look for a blockage OR starvation somewhere in the water inlet system, even the outlet as if it can’t get out, you have basically the same thing.


 His Come Back ;;;


  Hi, first of all, the impeller was totally fine.   It turns out this engine needs to have the water pump totally submerged and filled with water to function.   It didn't work in the five gallon bucket that I had laying around but it ended up working on my row boat.... go figure ahha.   Thank you for all the help and effort you put into helping me.





The number one requirement is to have a water flow into the motor.  All water cooled motors will have a water intake on the lower unit.  The older ones could have it through a screened tube in the exhaust housing outlet directly behind the propeller.  Later motors will have the intake through slots located above the prop but in the main gearbox housing, centered in the main (largest) section, and they will usually be on both sides of this housing.   These can utilize the "MUFF", which is a metal yoke holding rubber cups that cover these water inlets.  Usually only one cup will have access fitting to connect to your city water hose.


The older motors with the inlet behind the prop, will need to be ran in a barrel.

AND remember to turn the water on into the muffs BEFORE you start the motor, otherwise it is highly probable that you will ruin the rubber water pump impeller, (even if ran a few seconds).

With the above said, it is imperative to check these water inlets to be free of debris before you try to start the motor.  And as important, if you have it running but the motor is not peeing, before you get excited and tear it apart to replace the water pump, or just the impeller, CHECK these water inlet screens.   The earlier screens behind the prop, are considerably more prone to become plugged with weeds than the later motors, simply because they have smaller holes.


 What Make is It? ; Well sometimes you may be a bit confused as to the actual manufacturer.  In the older outboard motor identification, many were made by the more well known manufacturers, but sold through (usually at that time) mail order companies like Sears or Montgomery Wards. 

If it looks like a Jonson/Evinrude but carries a different name, it may really be what it looks like.  Under the OMC name, Johnson/Evinrude also  created a separate division, Gale Products Division at Galesburg, Illinois. 


Gale had their own Buccaneer brand sold by Gale dealers and mail order through Spiegel's,  they also made outboards for “house brands” such as Atlas Royal (Atlas Tire stores), Spiegle Department Stores under the Brooklure name, along with the Goodyear Sea-Bee.  They also made the following private brands: Sea King (Montgomery Wards), Atlas Royal (Atlas Supply – sold at Esso and others), AMC Saber, Hiawatha (Gambles Skogomo) and Sea Bee (Goodyear Tire Stores).

For the most part Gale motors had unique powerheads from their Johnson & Evinrude brothers. 


Many of these, shared engineering features such as the power head and lower unit/gear case but usually a year or two after the flagship lines.   Therefore spare parts may still be available for a comparable OMC model.

For more information as to other House Brands CLICK HERE.



Two Cycle Fuel ; cOne very important thing for you newbies to realize is that the motors we are referring to here are all 2 Cycle.  This means NUMBER ONE, the fuel needs to have lubricating oil mixed IN PROPER QUANITIES with the gasoline, in order to have any longevity of the motor at all.   This ratio is governed by the construction of the motor's internal bearings.  The older smaller motors may have bronze bushings for the main bearings and none other than the aluminum for the connecting rod.  The connecting rod bearings seem to be the critical ones.  The later connecting bearings could be updated to bronze also.  Then later, to needle roller bearings, with ball bearing main bearings.  The more efficient the bearing the less oil required.  Therefore if you blindly use the newer more common 50-1 ratio on an old motor requiring 24-1, your odds of seizing the motor and ruining it, go up considerably.


On these 2 cycle motors you have to mix the oil with the gasoline to lubricate the internal parts of the motor, so you need to know how much gas you will be needing, add the oil BEFORE you fill the fuel tank so that the oil mixes better than just dumping it in after you fuel up.  Small motors using the 3 or 6 gallon portable fuel tanks should not create much of a problem, as before hand, when you fill it, make you a stick gauge, by adding 1 gallon at a time, use a clean 3/8" or 1/2" dowel start filling the tank, mark the dowel at each gallon you add, then you can use it as a measuring stick.  This way you can refill a partly full tank with the known amount of oil.  By then measuring how much is in there and subtracting it from the tank capacity, you can know how much oil to mix. 


However if that is not possible, (usually with larger boats with a built in tank) then guess, add a majority of the oil of what you think it will take, top off the tank with fuel and then add the rest matching the amount of gasoline it took to fill the tank.


Fuel/oil mix on all the OMC motors that have needle roller bearings is 50 to1 of TCW-3 standard outboard oil.  Older motors using bronze bearings need a richer mixture.    When using the newer motors even with 50-1, if you troll a lot, your spark plugs may foul, simply because the motor never gets warm enough (up to it's operating temperature), therefore I have found that since I troll much of the time, other than getting there and back, I like to use a mix of 75-1 but of a FULL SYNTHETIC oil instead of the standard oil.  This gives me at least the same or better motor lubrication, plus it gives me less smoke at a troll and the spark plugs last longer before fouling.


A quart has 32 ounces of oil in it.  So for a portable 6 gallon tank to fill it using the 50:1 ratio would take 16 ounces, (1 pint) or 1/2 of the quart. 


 The formula shown below will be on all modern 2 cycle oil sold in the last 30 years or so.  On most all of the pints and quart plastic bottles of TWC-3 oils there will be a narrow clear vertical window on the edge of the bottles.  On the sides of this window will have numbers representing ounces and Milliliters for other parts of the world.  Or you can purchase special measuring containers showing different ratios and the amount of ounces needed.



Gallons of Gasoline

Gasoline to Oil Ratio

Ounces of Oil to be Added

16:1 24:1 32:1 50:1 100:1
1 8 5 4 3 2
2 16 11 8 5 3
3 24 16 12 8 4
4 32 21 16 11 6
5 40 27 20 13 7
6 48 32 24 16 8


The official OMC fuel/oil mix for most outboard motors in this year ranges has for years been 50:1.  This means 50 parts of regular gasoline to 1 part of outboard motor oil.  Remember that this was before unleaded gasoline or even possibly an octane rating that was listed at the pumps.  Now the recommended fuel is 87 octane gasoline. Early on for the 2 cycle motors the recommended oil was regular automotive 30 weight motor oil, then the outboard industry came up with any TWC oil, which finally evolved into the latest which is TWC-3 outboard motor oil.  You probably will not see much of the older TWC-2 oil out there anymore.  You can spend your money and purchase OMC oil for about $6.50 a quart, or buy a name brand quart for $3.59.  Sure the manufacturers want you to buy their oil, and for a new motor under warranty, it may be advisable to do so.  But the consensus from many experienced boaters is to use any good brand of oil, as long as it has the TWC-3  rating, it meets or exceeds the manufacturers specifications.  The TWC-3 represents,  Two cycle, Water Cooled, type 3 formula.  The formula 3 has decarbonizing additives designed to be more compatible with the newer non-leaded fuel.


So from the above information, you can see that fuel and oils have changed dramatically since these motors were first brought out in 1966.  In this instance, times have changed for the good, as we now have a better gasoline along with way better outboard oils.


DO NOT use oil designed for your weed whacker or chain saws as these AIR COOLED motors run a lot hotter than the water cooled outboards.   The water cooled outboards require the specially designed TWC-3 oils.


Run Your Motor Dry of Fuel or Not ;  If you do not run it a lot and let it set for months at a time, (ESPECIALLY WHEN USING ETHANOL FUEL), to keep the carburetor from becoming plugged with varnish (from that fuel) YES, it is a good idea to run the motor out of fuel when you quit, (leave it the water before you pull the boat out, or at home in a tank).   And pulling the fuel line, to run it dry is the best method.


Some say Yes, while others say No.  This will usually only apply to 2 stroke carbureted engines like we are covering here.  But the ones that say no are usually running a dual carbureted multi-cylinder larger motor.  Here the chances of one carburetor of running dry before the other is very possible.  When this happens, the motor MAY starve on one while running on the other carburetor, where the one cylinder that runs dry, could possibly produce scoring of that cylinder.  Remember these are 2 stroke motors where you mix the oil for INTERNAL LUBRICATION. 


So on these small motors that only have one carburetor, it will simply die when the carburetor runs dry.   It is best that when it starts to die (they will usually speed up seconds before it dies), at that point, choke it until it does die, this helps pull as much fuel out as possible from the carburetor.   In doing this, you may save a lot of grief (and expense to clean the carb) the next time you try to start your motor.


OK, Your Neighbor Brought You This Non-Running Gem ; If you are perceived as any sort of a marine mechanic, I am sure that you will be asked to help a friend with a motor that has sat for some time and/or possibly will not start.   Or sometime you may even acquire a motor that needs attention because the previous owner's patience ran out.  This section will deal basically with getting a motor running, and not fine tuning it, as that is covered on the "Normal Repairs" article.  Here will be my suggestions as to where to look and in the order generally accepted.  You are going to have to have at least the 3 main things functioning for you, they are all about equal in requirements.  If the motor has an electric starter, we will cover that later, but for now, it is assumed on the first part of this section that the motor will pull over with the recoil starter, but will not start.   I have had some use the words "will not pull or turn over".  In my mind this would mean it is seized, not that it will not fire.


The first law of trouble shooting is "NEVER ASSUME ANYTHING".   Has someone else tried to repair it, and is so, what did they do?  I suspect many of the used ones you see, especially on eBay or Craigs List may have been "repaired" by novices, or even experts with the outcome NOT BEING POSITIVE, so the owner gave up and is dumping his losses.  This could have been the wrong parts installed, which many times if a part is purchased off eBay, the seller may not really know exactly what he has.  The part may bolt onto your motor, but not function as designed.


If they, (the mechanic) did not know what they were doing, are the wires even going to the right places?  Are the ground wires making good connections?  Is the motor just in need of TLC because of negligence on the previous owners lack of outboard motor maintenance knowledge or has it been abused?   And while on the subject of wiring, for a standard tiller operated motor wiring other than kill wires are pretty well laid out.  All OMC (Johnson/Evinrude) motors using original factory wiring, will use either black or black with a yellow stripe for kill (ground wires), as on these motors usually the kill wire just grounds out the points or electronics, stopping the motor from running.


Don't totally believe what the previous owner told you about the history of the motor.  I purchased one motor that was supposed to have just quit.  Usually this would mean that the problem would be spark related.  When I got into it by pulling the flywheel, there was dry, redish brown rust on the outsides of both coils, indicating that the motor had laid on it's side in water over the winter enough to get rusty after the water evaporated or the motor was retrieved.  Compression was 62# and 105#. 


With the head off, it was evident that this motor had been immersed in water in some way for a considerable length of time.  Maybe not dunked in the lake, but my guess in the bilge of a boat in the back yard without a cover, rainwater filled up enough to get into this motor.  With the head off, both cylinders were hosts to LOTS of rusty and carbony oil.  This excessive amount of oil could not have gotten there from inside the motor, it had to be squirted into the spark plug holes trying to free it up. There was also evidence of the use of LOTS of starting fluid that had a red dye in it around the carburetor in apparent failed attempts to start it. 


The thermostat was missing also, why is any ones guess.  The electric starter was rusted so badly that it was seized up to the point that it was just scrap.  The lower unit had fish line around the prop shaft in front of the prop enough to cut the rear prop shaft seal out, there was NO oil in the gearcase and after flushing it with kerosene a couple of times there were metal filings along with brown rust in the bottom of the drain bucket.  The prop shaft could not be pulled out, in that the internals appeared to be effected by saltwater so the whole gearbox/lower unit was also scrap.  The driveshaft was also frozen into the pinion gear and could not be removed.  The trolling idle screw assembly was missing.  One transom clamp screw was almost there.  The picture of this block with the head off is shown below.  The previous owner had told an untruth and withheld many others in order to hopefully gain a little more in dollars in a sales transaction, where obviously the $200 that I paid for it (from the second party) was way too much.  Also don't take the word as gospel of a friend in buying of trading boat motors, wives or horses.


These are all clues that you will have to consider in being a outboard motor detective.  Sometimes the word "Detective" and "Mechanic" are closely related in cases like this.


Think about this, if you still work for a living, consider the following:   How many free days a year do you have?   Of those how many are available for fun (spelled fishing/boating)?   Of these left, how many will the weather cooperate and finally then will your motor run correctly or at all, or will you spend half the day or more trying to get it running while wishing you were on the water?


Some people who own boats and motors may also be mechanically challenged.  If they have tried to do anything to it without the slightest clue as to what they are doing and then bring it to you, are you up to the challenge?  These are the people who should not be left alone with a dull knife or even a pencil sharpener.  Long ago, I sold a 12' boat and 1958 10hp Mercury motor to one of these guys.  He ran it onto a sandbar the week after I sold it to him, ruining the water pump impeller (faulty impeller-my fault).  OK, I replaced it at no charge.  Two weeks later it would not run right, but he could not explain the problem.  I went fishing with him and on the river, (mainly because he was fishing an area and for a specie that I wanted to learn) it ran so bad that we tied up to a overhanging tree, and there on the water, I tore the carburetor apart, cleaned and re-adjusted it.  My comment to him was to keep his dip-$hit fingers off anything other than the starter rope, throttle and/or shifting lever.


Years later I had a similar experience but with a 10hp Johnson, the motor ran when I traded it to him.  I had to later take it back for because he was afraid the motor would burn up since it was not peeing fully (the pee hole tube became unconnected under the cowling).  It was running good when I delivered it to him the second time.   Then more problems, but this time it was the fuel pump going bad.  Every time it was running fine when I delivered it to him.  Again it came back, this time, my fault as apparently I did not push a points output wire down far enough into the timing plate and the flywheel wore through the wire insulation, grounding it out, killing the motor.  On this one, a bunch of bad happenings to an old motor and it was about time to change and trade another newer motor.  I guess a lesson is to really consider is whether you want to trade/sell to a friend who may not totally understand outboard motor functioning.


Never pull any manual start motor till you wear blisters.  You will only wear out your body, get frustrated, but also put wear the starter as well.  If it isn't running after half a dozen pulls, there is usually something wrong with it.  OR you are doing something wrong.  So, stop pulling, and do some research.  AND ESPECIALLY ON THE OLDER MAGNETO IGNITION MOTORS, pull that rope starter as if you were mad at it.  The faster the flywheel turns to generate spark, the greater the spark is created to the spark plug, and hence the easier it is to start.

Diagnosis ;  This article started out pertaining only to the OMC 9.9/15hp motors, so it will still lean that direction, but I am trying to incorporate other models as well.  However the principles are pretty much the same for most outboards, especially the older OMCs (Johnson and Evinrudes).


In making your diagnosis, first, I would make a list of known/suspected problems.  Then another list of known previous repairs, if possible.  Then a check-off list of things you have checked, with an OK or possible need to re-check behind that.  Don't take anything for granted, even LITTLE things like hidden electrical connections that may be corroded.

The next step is diagnosis.  Never start pulling parts off, or apart until you have a good idea of what is wrong (other than pulling the spark plugs).  You can make things worse, then you will have multiple problems where you will not be sure which was then actually the culprit.  We can only guess what the problem is from here.  Makes you appear smart to start with, but doesn't fix the motor.  You need to do the basic outboard motor health check.  If new to you take numerous GOOD close-up photos of the wiring, fuel lines etc.


Sometimes initially it may be hard to distinguish electrical between fuel supply problems, especially if you do not know why it died (like being brought to you as a dead motor).   It is easier if you were running it and it died.  My method of distinguishing the difference is, if you can squeeze the fuel primer bulb and it restarts, (or if running, picks back up) you have  a fuel SUPPLY problem.  If you can choke it and it comes back, you have a CARBURETOR problem.  If neither of these help then it is probably an ELECTRICAL problem.  Now this being said, IF there are other major issues, those need to be addressed beforehand.  Again be a detective.

1. Spark, adequate spark at the right time.
2. Fuel and air in the correct amounts.
3. Adequate compression
4. In addition, but not normally taken into consideration, a two-stroke needs vacuum/compression in the crankcase.


Spark, pull the spark plugs and inspect them.  If they look clean, replace and proceed.  HOWEVER , if there is any question, REPLACE them with new ones.  There is no sense of chasing your tail trying to diagnose a problem and all the time it was a bad spark plug.  These are not expensive and good insurance.  If in doubt of where to buy new ones, take your old one to a automotive parts store as a sample.  Do not just put in any old plug as the length of the threaded section is critical, too short will foul easily, while too long will hit the top of the piston.

It is best to trouble shoot fuel delivery issues starting at the the tank and this doesn't mean just the connector, issues inside the tank can cause a lot of grief and cost money that doesn't need to be spent.   It's a simple procedure to put an open ended line, in a tank....or jerry can, pump up the primer bulb, run it, and see if it changes anything.   9 out of 10 times, a simple problem gets turned into a major unknown issue....that's as simple as an o-ring / hose clamp etc etc.

1.The fuel line from the disconnect fitting to the pump has gotten hard and is leaking air.  Solution is replace the line and use new small hose clamps on it.

2. The fuel line from the tank to the engine has disconnect fittings on each end, Do you have it connected properly?  There will be a large arrow on the primer bulb, this points to direction of the motor.  Both of these quick connectors have neoprene O-Rings inside the connector where it slips over the fuel line studs on the tank and motor.   These O rings in the fittings can be damaged, leaking causing a vacuum leak up to the motor.  Solution is to remove and replace the O rings, (however there are 3 major manufacturers of these quick connectors and they all use different O-Rings, along with the fact that most are not identified by any manufactures name (maybe a code number that means nothing to you or me).   If you can not identify the connectors and the hoses/primer bulb is pliable, replace the fittings with new ones, or buy a whole new line with fittings and bulb.

3. Pull the fuel line off the carburetor and with the tank connected to the engine and pull starter rope, rolling the motor over.   Fuel should come out of the line that went to the carburetor, indicating a good pump.

If you are using an aftermarket tank, we know you are leaving the tank vent open, right?  


Or are you using the right fuel line?  Yamaha connectors look the same as OMC, but the fuel stud is larger, creating a air leak.  A Yamaha line/connector will fit a OMC tank/motor, but will be so sloppy a fit that it will not function.


Before we get real carried away here, was the last gasoline used the ethanol type?   If you leave old ethanol fuel in the carburetor and don't run the motor dry, it can create a gooey mess inside if left for some time (like over the winter without stabilizing the fuel beforehand) which will need to be cleaned out.


Another thing, you should consider is finding out a bit about the motor that you are staring at BEFORE you start unbolting things.  Number one would be, are any spare parts available??  If not, you may be spinning your wheels, getting it partly repaired only to find further needed parts are not available and now you have both time and money invested on scrap iron.  A thing many do not realize is that some outboard motor manufacturers may have a higher grade and a lower grade line of motors.  The lower grade may be the ones with fewer spare parts availability.  The distinction can be only paint, electronics or fuel injection, with most of the other parts the same as corresponding motors.


In the late 1980s Mercury wound up buying the old outdated West Bend / Chrysler line of motors which they labeled their Force brand.  They later decided to spruce them up and improve these Forces, with Mercury gear cases/props, CD ignition systems, etc., and market them as 2nd tier engines.  The understanding was that they were actually pretty good, though not really hot performers but performed fine as a second tier, "cheapout" image for the owners.  This situation spooked Yamaha and OMC enough that they downgraded their own lines, removing oil injection and other items, so they, too, would have a cheaper second tier line.  OMC called them the "Special" engines, with odd ball HP number to set them apart from it's parent motor like a 14hp or 33hp as compared to a 15hp or 35hp.  Yamaha did basically the same and had a different model designation for theirs also.


(1)   General Appearance ;  Here you should generally get a real sense of what you will find as to the care, or non care the motor was subject to.  Take a look at the overall motor, sometimes scratched paint can be deceptive, but if the owner had no pride in ownership even as to scratches, look farther.  Pull the upper cowling off.  Look underneath it for signs of oily residue.  If the rings are bad, you very likely will see an oily film on the inside, especially near the carburetor intake as shown in the photo below.


Has the fuel line rubber bulb became hardened over time to the point it is hard to squeeze?   If so, you will need a new fuel line assembly.   Beware of fuel tanks setting out in the rainy weather.   Are there any little kids around, if so check inside the fuel tank for rocks, sticks and mud.


With the shifting lever in neutral, give the twist grip handle a twist it, if there is a lot of slop here, you may not be able to maintain a throttle position setting without holding onto the handle all the time.  With the older OMC motors from 74 to 85 that utilize the gearing on the throttle shaft, this takes a lot of time to cut plastic shims and to fit them to get proper tension if everything is worn.  The 86 to 2006 OMC cable throttle type are not usually prone to this problem.


You might find a gem that looks bad, but only needs spark plugs, clean fuel, but looks ragged, but the odds are not good in a case like this.


Oily residue on the inside of the upper cowling should be a clue to something not exactly right. Evidence of an inoperative water pump impeller, look at the discoloration (dark brown burned paint) of this overheated head

(2)   Spark ;  Pull the spark plugs and look at them.  If they have not been recently replaced, are they black and oily or just a gray color?  They will usually be slightly oily and possibly fouled if the motor is used mostly for trolling may not get warm enough to totally do good combustion since this motor uses an oil mix in the gasoline.  If it is dry and a gray color, that is good.  


Spark plugs need to be gapped properly.  Most are just fine out of the box, but in troubleshooting, check them first.  I got caught in this once, guy brought a motor in, it ran at a idle fine, but speed it up to about mid throttle it would lope, (miss-then restart repeatedly).  The plugs were new so I did not look at them, but after tearing the carburetor apart 3 times, I finally found the plugs were gapped at about .012" instead of the recommended .030" for about all outboard motors.


You can clean them, the best is with a sandblaster.  Spark plugs for these motors are reasonably priced (about $2.50 to $3.50 each) and it may be beneficial to purchase a couple of sets.  Then you can have a new set, clean the others for spares.  You might consider vacuum packing them if for longer dry storage if you plan on keeping them on the boat.  This will assure you that they are clean and dry when you to need to use them, especially if you are near saltwater. 


If a motor is running, but lacks of power, it is usually the result of only running on one cylinder.  It is suggested to start it up, bring it to a fast idle and with a pair of insulated pliers, pull one spark plug boot at a time.  The motor should be able to run on only one cylinder, so if you pull a plug and the motor dies, you know that the other cylinder was never firing or running was weak.


Here for the OMC motors, I will make a distinction between magneto ignition (points, condenser ignition) and electronic ignition in relationship to spark plug types.  These points ignition system give a weaker spark (and seem to get weaker as they age) than the post 1977  CD ignitions.   It is the experience of many that the pre 1977  OMC 9.9/15's had a very weak spark to begin with.   It has been found on these pre 1977s that by switching to NGK B6HS spark plugs (and in the next higher heat range) the fouled plugs go away and the engine runs better.   If you have to use Champions, then possibly the  UL81C would be a second choice alternate.


OMC finally got this right when they went with Capacitor Discharge electronic ignition.  


If your spark plugs repeatedly foul you could have a combination of things happening.  Check to see if the thermostat is still there, (some people pull them out).  If the thermostat is missing, and you are using it mostly for trolling in cooler climates, the motor is not getting hot enough for proper combustion.  It might be a good idea to run Sea Foam thru it to decarb the piston and rings.  Then for some reason, the recommended Champions plugs may foul out with very limited usage on the magneto ignition system. 


These later OMC post 1976 motors seem to run best on Champion L77JC4's, than any other brand.   Normal gap settings are .030, however the old time mechanics say that for doing a lot of trolling you might re-gap them to .040 for less fouling. 


This paragraph was snatched off Champion's website.  "Outboard marine Capacitive Discharge Ignition systems (CDI) such as used on some Johnson and Evinrude marine engines require a special inductive type resistor (such as the Champion Q-type resistor).   Use of non-inductive resistor type plugs on these motors can cause misfire and poor performance."


You may be able to check for spark, by pulling the spark plug from the head, and reinserting it in the plug boot, then ground it, (holding the metal plug body against some metal part of the motor), while pulling the starter rope.  Here, you need to have made a good connection of the spark plug to the motor, (somewhere where the paint is not insulating your connection).  You should be able to see a blue spark jump from the center electrode to the over-arm on the plug's metal threaded area.  It will not shock you, UNLESS you happen to touch the exact area of the spark jumping.  However this spark may be hard to see if you are alone and in bright daylight plus having to pull the rope yourself AND look for the spark while the motor happens to be moving slightly.   Have both spark plugs out also helps lower the compression.  Here is where you may need the help of the wife or a fishing buddy.  And it only tells you that you have minimal spark, you really need a spark gap tester to really verify the actual amount.  These testers are cheap and readily available from automotive stores.


Another thing I would look at is the flywheel key sheared or semi-sheared?   See section below.   Here you can get spark, but it may not be timed correctly because the flywheel may have slightly slipped on the crankshaft, changing the spark timing.  If everything else looks good, and it will not fire, this is the first and simplest thing to look at.


If the motor is a magneto style ignition and everything looks OK, but will not start, look at the points breaker cam on the crankshaft.  There should be a word on the top of this cam that says TOP.   If you can not see this, maybe someone installed it upside down, which will surely effect the timing.  These cams just slide onto the upper end of the crankshaft with the flywheel key being used for the proper alignment.  However on the older motors, this word TOP may not be there, if so then most of us use the crankshaft key as the set location as it is usually located at the thickest part of the cam.


If this spark is hard to see, you can make a simple spark jump tester as shown below on the left, out of a piece of 1" X 3" X 6" wood, (2) 1/4" x 3 bolts, double nuts, a piece of aluminum, wood screw, wire with an alligator clamp on one end.   Cut out  2 large holes, drill (2) 1/4" holes in the bottom center.  Grind a tapered point of sorts on one end of each bolt.  This tapered end goes up or the one that the spark will jump to the aluminum plate from.  Thread one nut on the bolt push it thru the hole, place another nut on top, then when you get the distance you want, tighten the lower nut.  The actual gap should be  7/16" to 1/2" for the electronic ignition and 1/4" for the points and coil type, you can adjust it to what ever gap you want to the aluminum plate on top.  Take an aluminum sheet and drill one hole in the center that will be used to attach the plate and the ground wire.  Cut off the bolt head, deburr it so it will slide into the spark plug boot.  You may want to use a black electricians tape or dark paper glued to the back side at the intended arc point so you can see the arc jump better.


For the price of under $10.00 you can purchase a ignition spark tester from Car Quest part number STL 50850 as shown below on the right.  This unit has a threaded rod adjustment that has a turned end to match a spark plug outer end, a spring clamp that can be attached to a wire or small bolt head for a ground.  This rod can be adjusted to what ever your heart desires.  The body is made of a plastic so it does not short things out.  The instructions say you can test the spark without  removing the spark plug.  Well this may be true with a car or a outboard that has electric start, but for a person to try to use a rope start, watch the gap at the same time, not very easy.  The one thing I don't like is that the spring clamp can not be opened enough to fit a 1/4" bolt head without becoming disjointed.


In use of the home made tester, pull the spark plug boots, position them on the 2 protruding bolt ends, clamp the alligator clamp onto an exposed bolt head.  Pull the starter rope as if you were trying to start the motor.  You should see the spark jump between BOTH  the points to the strip for each cylinder.  If it only jumps on one then you have a coil bad or possibly a bad ground connection at that coil, or even inside one of the rubber connectors or the spark plug boot.


The older point/coil ignition the spark jump will probably be near 1/4" for that style of ignition.  For the electronic ignition 7/16" to 1/2" spark jump is about right.


 Improvised spark tester

 Car Quest tester #STL 50850


Spark alone does not do any good if you have a scored cylinder or bad rings creating low compression that also leads to fouled spark plugs.  Check your compression by pulling both spark plugs, screw a compression tester into one spark plug hole and pull the rope starter 5 times RAPIDLY (AND like your were mad at it).  The factory does not give any recommended compression numbers, but from my experience I do not like to see anything lower than 75#.  On new rebuilds, it is possible to get 125#.


One more thing to look at is if one is high and the other is low, this imbalance is not good.   OR if both are exactly the same, which could mean a blown headgasket between both cylinders allowing a balance of pressure from one to the other.


If it is hard to start, and the spark plugs are wet when you pull them out, that may be a indication that you have a blown/leaky headgasket into the water jacket.  Or again look at the spark plug condition, if there is any doubt, replace them.   Low compression and oily spark plugs go hand in hand because the fuel/oil does not get burned efficiently, creating black oily carbon, where this accumulates in the cylinder/piston/head where the spark plugs are located.


Also if you get intermittent spark or only firing on one cylinder, you may have a bad connection at the boot end where the boot goes over the spark plug.  Pull the boot straight off the wire and cut off enough of the wire (about 5/16") and push the plug's wire coil back into the wire, then reinstall the boot.  In the photo below the insulation has been stripped off showing the arcing from the contact point to the wire.  A little may be normal, but once it gets this bad, you loose conductibility.


Here a initial test if you get a non-firing cylinder, is to use a Multi Meter and test the wires on each end for conductivity.  It may be a bad connection like seen in the photo below, or even a broken wire.

If you have to replace a spark plug wire, be sure that it is NOT the automotive graphite suppressor type wire, but metal cored.


Notice the the arced, burned wire at the location of the coil's  contact  point


Also somewhat akin to the above situation, check the condition of the whole spark plug wire, even to pulling the timing plate so you can see the part of those wires underneath and running to the coil.  Sometimes on the older motors, this wire may have been shortened at the plug end enough that when the timing plate is rotated to FAST, the wire is so short that it can partly separate the insulation thereby creating a short or even it may still be close enough to make connection at slow speed but not at fast speed.


If you have done most of your suspected repairs and still no fire when you pull the starter rope, you may try pulling the starter rope in the dark of night, as any leakage or jumping of spark will show up way better in the dark.


Another thing, rather rare occurrence, but it is possible that your kill button may be defective and grounding out internally.  This would be more likely to happen on the 1987 and later motors using the "Man Overboard kill type switch" that uses the lanyard, because there is a internal spring pushing the button out.  If something plastic internally broke, the button my still be out, but shorted out internally.  For a test for this, pull the connector for the black with a yellow striped wire and disconnect this wire.  This may also be hard to trace this wire down on the post 93 models because of the wiring harness inside the tiller handle and being buried under and around the powerhead.  This would probably not be the case with the earlier pre 1977 kill buttons that are on the front cowling.


If the motor is a 9.9/15hp between a 1974 to 1976, the ignition system is the older points and condenser type.  These coils and condensers can get weak over time, may have spark, but a yellow instead of the hotter blue.  Or the motor may start, run for a few minutes, then die.  It will not usually restart for about 1/2 hr until the condenser cools down.  What may be happening is that internally in the condenser (which is simply thin aluminum strips wrapped with waxed paper between them into a coil that is encapsulate into a metal container) the waxed paper may be slightly deteriorated, when the energy is created inside the canister, the aluminum expands slightly, where the paper is thin, will short out.   After the aluminum strip cools, and pulls back the motor may restart.   If this is the case you may need to replace the condensers, and possibly the points as if the condensers are failing, they put lots of undue burning on the points, but the coils hardly ever go bad unless the outer insulation cranks so bad that they arc out to the base. 


Another thing that can happen on this style of ignition is that if the individual coils may be getting weak, do give off a spark to ground, but with everything together, may not have enough juice to fire the spark plug UNDER compression as the compression blows out the fire.


A test to try to get it running if the coils and condenser is getting tired, would be to reset the points to a larger gap. say even up to .030, which will make the plug spark hotter, possibly firing it.  This however is just a patch and not the cure to the problem as it will also make the timing off.


In the photo below you will see the blue insulation worn off one of the points wires.  The gray color at the point of the arrow is the wire itself.  This was caused by that wire protruding too high and the flywheel magnet boss rubbed through the wire's insulation, effectively shorting out and killing that cylinder.  This motor ran fine until the wire insulation got worm through, then it ran only on one cylinder.  The cure was to seal the bare wire and then re-route the wire behind the inboard boss.


The red arrow indicates where the flywheel magnet boss wore through the points wire


(2 1/4)   Flywheel Key Sheared Off :  In you initial diagnosis, if you have no spark, you may have a sheared flywheel key.  Sometimes it the flywheel nut was not tightened properly, the flywheel will be loose and wobble over time, then become looser, which could lead to the key being sheared off even with the surface of the tapered driveshaft's upper section.  Or if the motor is running fast on the boat, and the motor itself hits a solid object, like a rock or log, where the motor stops, but the heavy rotating flywheel keeps going, shearing off this key.  This flywheel key is what locates the flywheel in reference to the location of the pistons, which produces the ignition timing or firing the power to the spark plugs at the right time for it to run.


These keys will usually be sheared pretty close to the tapered crankshaft.  They are made in a 1/2 moon shape, so when sheared off you do not have anything to grasp ahold of to remove one.  About the only way to get a broken one out is to modify a punch that is very close (smaller) in width of this broken key, (use the flywheel slot as guidance here).  You should be able to tackle this job without removing the timing plate.  You do not want to wedge it in so bad that it will have to be drilled out (about impossible).  Since the slot in the crankshaft has a radiused bottom, you can, by carefully aligning your punch on the to edge of this broken key, drive it IN and Down, which will rotate it slightly out at the bottom.  Once it starts to move, hit it again, forcing it farther out at the bottom.  Finally you should be able to by using a pair of locking pliers to force it up and out.  If you happened to burr the slot, you may have to clean that up with a file.



In setting these points, the manual says to advance the twist grip throttle to FAST as far as it will go, however I do not see why it would make any difference.  Rotate the crankshaft so that the #1 piston is at Top Dead Center.  This can be verified by pulling #1 (TOP) spark plug, by using a flashlight, rotate the crankshaft clockwise until you can see the piston come up, go slowly, backtrack just after it starts down.  The word TOP could be on the top of the points cam, but TOP only applies to the side of the cam goes up when assembling.   The proper position to setting the points should be near the SET position.  If the word SET is not there, then use the flywheel key as the location.  The keys will always be in the thickest part of this cam, meaning also the highest position.  


Without changing the twist grip location, move the crankshaft to the SET position.  Set the #1 points (on the RH side of the motor) with a feeler gage at .020, rotate the crankshaft 180 degrees, again with the rub bar at SET, repeat the setting for #2 piston.  The points surface should be free of oxidation, not have corrosion.  If the points are set off by .0015, this could change the timing by 1 degree.  So it is important to get both set of points set as close to the prescribed setting as possible.  CLICK HERE for a link to an article on ignition timing for these older magneto systems.


One thing that you may run into on the older motor replacement points, the felt for the cam oiler can be too long in some sets of points.  If it extends under the rubbing block area, this can hold the points open.  Some of the older cams have a spot imprinted that says "top" while others (usually later motors) says "set".  And it's easy to get the green coil wire trapped between the bottom of the coil body and the bearing area of the timing plate, shorting it out.  The wires need to be isolated from the frame by the fiber washers in there.

If the points contacts do not look corroded or pitted, take a piece of business card with some rubbing alcohol or electrical contact cleaner and run it through the points once or twice.

If you have replaced the condensers and it refuses to spark, you may have gotten a couple of bad condensers. Try your original ones just for giggles.

Also, check the stator/ timing plate for lateral play.   Move the flywheel clockwise by hand and look for any jumping of the plate.    Pull the starter rope, check to see if when the flywheel is rotating that the timing plate moves sideways when the flywheel is rotating.   If it can wobble or move laterally, it WILL change the point gap!   Make sure once the plate is stabilized that the points are set at EXACTLY 180-degrees opposite each other.   Check your TDC by a rod in the spark plug hole and time it so the piston is at the top of it's movement.  This is Top Dead Center for that cylinder.  Set your points timing for both cylinders this way so that you get each timed to the piston TDC as the timing mark on the crankshaft is not precise enough.    Those point ignitions systems worked alright when everything was right but did have issues with fire if things were off even a little bit...


I have also encountered one of these older engines that even after sandblasting a set of spark plugs, I could not get a test firing to ground across the contacts.  I did however notice that there was a couple of smaller sparks jumping down inside the plug.  Replaced it with another sandblasted and cleaned plug, but still only run on one cylinder.  I then pulled the plug wire while it was running on the other cylinder, inserted the "BAD" spark plug in the wire boot, held it to ground and I got about 5/8" of bluish spark, but then pointed it to the plug still in the head, no change in the running.  I bought new spark plugs and it started.


I came across a puzzling situation in a 1974 motor which had electric starting charging coils, when I replaced the points and condenser, I lost fire to #2 cylinder.  Upon investigating, I found that these aftermarket points were not really compatible with the one of the electric start charge coils.  Number 1 points has lots of room as seen in the photo below.


The points spring tension retaining screw protruded so far out that it grounded out against the coil body.  I even tried to slightly bend the point wear arm, but could not get it far enough without ruining it, to clear the screw head on the back side.  I then ground down about 1/2 of the screw head and obtained about .040" clearance.  Next I cut the top out of a plastic margarine tub to form a insulator and siliconed this plastic in place against the coil body.  Just this clearance may have been OK, but this provided a greater degree of isolation.   First pull, it started and runs OK afterwards.


The red arrow indicates where shorted out screw head is.  The arrow tip is actually on the silicone with the plastic just below it.


Another thing to look at are ANY wiring connections.  You may have to do a continuity test on each wire.  On one motor (again the 1974) I found the wires coming from the points to the coils outside the flywheel area had corrosion, would only allow the test light to come on if the connections were twisted just right during the testing.  What I found after cutting off the wires at the quick connectors that the individual small wires in the main wire bundle was oxidized so bad at the end that I had to cut off another 1/2", then scrape them to get a better connection inside the crimp.   I then replaced the old quick connectors with the newer "bullet type".  On these old points type check any solder connection, as the solder may look OK, but the wire may be frayed below and lack enough wire to conduct enough fire.


It may also be well to consider checking the wiring connection inside the spark plug boot, (out of sight - out of mind).  This might also be the time to replace the spark plug wires if you are having ignition problems.  However if you do, it will is important to use marine copper wire instead of the newer automotive carbon type wire.


Also there is one or two wires going to the kill button.  If the older points type ignition, (shown on the photo below on the left) the 2 blue wires coming from the coils/points, also Y off which go to the kill button.  The red arrow points to the connector to the kill button.  It appears that when activating the kill button, you just short the 2 coils together, killing the motor. 


If the newer electronic ignition, shown in the photo below on the right, one wire (usually a black with yellow stripe) comes from powerpack to the kill button (RED arrows below on the right).  The other wire (usually a black only) goes to ground (BLUE arrows). 


To further explain, of the bundle of 4 wires coming from the powerpack, the Orange/Green striped wire (# 2 coil) and Orange/Blue striped wire (#1 coil) (YELLOW arrows) go individually to the appropriate coils.  Of the other two wires, one, a black wire is grounded (usually under a coil bolt).   In the case of the 1992 shown below on the right, the hot wire black/yellow striped wire that goes to the kill switch has a in line rubber connector.  One wire from the kill button is also grounded under the same coil bolt.  The wires from the kill button on this motor happen to be dark blue.  Some years of motors may be slightly different, but basically you are shorting the powerpack to ground, killing the motor.

Check these to be sure the kill button is not stuck and shorting out if it is the front cowling mounted version, or that the lanyard clip is in place if the later lanyard type kill switch on the tiller handle.


1974 to 1976 OMC coil & kill wires from coils 1992 OMC coil & kill wires from powerpack


If you get intermittent cut out and die after the motor has run for a bit on a post 76 motor with electronic ignition, you can not find the problem when doing your testing, try heating the powerpack up with a hair dryer with the motor running on the muffs and see if it repeats the problem which could be losing spark.    It could be either the powerpack or the coil, so try both.   Something is failing when it gets hot (either by from the heat of the motor or from heat from the electrical input/output), this would be normal if total failure is just around the corner. 


Another thing if it dies after it has started or ran a while, do a spark test when it does not want to restart.  I suspect you have an electrical problem, and more than likely at either the coils or powerpack.  When these electrical components get older and start to fail, at a cold condition, the internals are cool when the windings are separated by insulation.  If the insulation starts to break down, as it gets warm because of the voltage/amperage going thru it to create the power to the spark plugs the windings expand and short out.  When it cools down, things are back to normal -- For A While--   Once it is running, it may stay running unless it is slowed down considerable or stopped.  And it just gets worse.
Any good marine repair shop should be able to do a test on either of these components.

OMC lists the same powerpacks for the 2 cylinder motors as being used for from 6hp to 55hp motors made from 1977 to 1982.  However the wiring boot may be different depending on the year of usage, as the kill button wire is separate on the older models.


To do more testing, using an inductive automotive type timing light, alternately clamp on to each plug wire and watch the flash.  If it doesn't vary in frequency or light intensity as you hit the "runs like crap" zone, then your ignition is doing all it can.  If it skips and dims, you still have problems with the ignition.   If so check the stator/timing plate moving freely with the throttle, yet not overly sloppy on the base?


I had one motor that would not fire on one cylinder when it was cold, but after it ran a while the other cylinder would kick in then would then run OK.  This is just opposite of what you would expect if a coil or electrical component was bad.   I had changed plugs more than once, tightened the coil bolts, checked the high tension plug wires, checked the connector wires for corrosion among other things and was about ready to tear my hair out.   I even cut a fishing trip short by a few days because I did not want to get stranded in the bay with the wind blowing.  


It was traced to #2 coil not having any output to the spark plug.  I finally swapped coil input wires from the powerpack in the rubber amphenol plug connector boot, electronically changing the coils.  The #2 plug now fired, but the plug wire from the old #1 coil was now dead.   I then replaced the wires to original positions and replaced that #2 coil with another known good coil.   Same results, no fire to #2 plug, so the original #2 coil was OK. 


This then was starting to point to the powerpack, but when they do go bad, they usually just die for both coils.  It was getting late in the evening and I wanted to get the problem taken care of and with the motor still running on the muffs, I just happened to look at the side of the powerhead, there was blue arcing off the bottom powerpack bolt.  Upon checking, I found the bolts holding the powerpack to the block were loose, not creating a good enough ground.   Why this condition only effected the #2 coil, I will never know.


In my mind I knew it in all probability was a bad ground, but where, I would probably never have checked that bolt without seeing the arcing in the dim light.   The good Lord does look out for us shade tree mechanics sometimes.


On the above motor after tightening all the ground wires, this motor still acted up as before.  All the tests still pointed to the powerpack.  I bit the bullet, bought a new powerpack and problem solved.  I suspect that since it took many fishing trips over a period of 6 months, thinking I had found the problem after each time, that one output wire or diode from the powerpack had become internally partially shorted out because of the loose ground under the one coil.


Another 9.9hp motor (a 94) had been my trolling motor for 3 years, but was replaced by a Yamaha T8 4 stroke because in my old age, I needed a power tilt motor.  The Johnson sat for 3 years, but would not produce any spark when tried to start it then.  This motor appeared to be running fine when it was removed from the boat. Testing was done and the powerpack was bad.  I replaced the powerpack. I then traded it off to a friend who lived near the beach, only to have it die on the new owner.  No spark on either plug.  When I got the motor back it was really hot weather, I let it set for a while as I loaned him a different motor.  From all indications it pointed to the new powerpack failing.  In my preliminary testing the first thing was to check spark AGAIN, spark OK on top plug, where it wasn't a few weeks before.  Check the bottom plug for spark, it was OK.  Maybe the could were not being grounded properly, so when I pulled them off (this model had both coils made together as a dually unit).  What I found was the back side of the coil where it was sealed around the hard rubber housing, that the rubberish sealing had came loose and even had evidence of something being corroded inside, forcing the sealant out and away from the body.  I bought a new coil assembly and that solved the problem.   My guess was that in his high salt air moisture environment that there was just enough moisture inside to short things out.


For those of you who use a remote control and therefore a electric choke, this electrical diagram for the electric starter is not shown, apparently the factory considers this an alteration of sorts.  All I can say is that the electric choke is simply a wire from the switch, relaying power to the choke solenoid.  If that is OK then check that the solenoid is grounded.


The thumbnail photos below are for the OMC 9.9/15hp motors.


Electrical diagram for manual starter motor Electrical diagram for electric starter motor
Click on the above thumbnails for larger picture


All OMC (Johnson/Evinrude) motors using original factory wiring, will use either black or black with a yellow stripe for kill (ground wires).  For remote controls that use a key type ignition switch, the letters on the rear of this switch being (M) and possibly two of these M lugs used for the kill circuit, will as above, have either both black or a black and a black with yellow stripe. (B) will be the battery wire and be red or red with a purple stripe.  The (S) or start lug will have a yellow wire to the starter solenoid.  (I) lug will be a hot 12 volt wire to anything needing power and will be a purple wire.  (C) the electric choke will be a purple with a white stripe wire.


On OMC motors made from 1987 and on which have the kill button on the tiller handle, if either of the clips shown below are missing the motor will not start, kind of like turning a key OFF.   There are 2 variations of this, the one shown is from a 1987 to about 1990, which as it on the end of the twist grip throttle handle.  After that, the clip was moved to a separate switch about 1/2 way up the handle, while retaining the smaller twist knob as a slow speed limit control.


OMC's restart clip for 1987 & newer motors


The above illustration  and the following information are a reprint of OMC installation instructions for "OMC Clip Assembly P/N 431808" dated 3/87.  This part is also known in the parts manual as (Restart Clip).  "This clip assembly is for use, under limited conditions, on models with an Emergency Ignition Cut-Off Switch located in the steering handle.  Make sure that you are aware of the purpose and benefits of the Emergency Ignition Cut-Off  Switch  as described in your Owner's /Operator's Manual before disabling.


Outboard motors used in certain applications, e.g. auxiliary power on cruising sailboats or as a trolling motor on larger fishing rigs, may not be able to take advantage of the benefits  provided by the Emergency Ignition Cut-Off  Switch feature.  For applications such as these, the cut-off switch can be disabled by replacing the clip and lanyard assembly (A) with the OMC Clip Assembly (B), as shown.  The clip (B) will disable the cut-off switch while retaining the "PUSH" Stop Button feature.  If the motor application changes, reactivate the cut-off switch feature by replacing the clip (B) with the original clip and lanyard assembly (A)".


Stators are a weak point with the OMC's.  But then, if its still running good, leave it alone.  You will find that about 8 out of ten stators will have that brown goo leaking out of them after a few years of heat. I haven't really seen where its made a lot of difference.  If you want to check the voltage to see if its up to par, check the AC voltage between each pair of brown wires going to the CDI.  The book calls for 130 volts but then I've seen them still run with voltage as low as 85.  They may be resisting a tad bit on starting however.


(2 1/2)   Kill Button :  For most of the older motors with a magneto ignition, you will not find a kill button, as they employ the simple method of retarding the ignition timing so  slow that it does not run.   This was changed on most about the time the electronic ignition came into being.  And on the OMCs the wiring is backwards from most would think as to run the circuit is OPEN, apparently to conserve on the battery when not running, so you do not have to disconnect the battery if put into winter storage..  The kill button only shorts out the wires to ground to kill it.  Once it dies, the circuit is open as the kill buttons have a internal spring to keep it open.


(3)   Fuel :  For motors to run, it has to have an uninterrupted supply of fuel AND air in the correct proportions.  If all else fails, and the motor is in good shape, it should start by being artificially being fed fuel.


First, be sure there is enough fuel in the tank to cover the internal suction tube or you will be sucking air part time, which will loose vacuum to the fuel pump.  On theses single line fuel systems, the primer bulb acts as a manual fuel pump sucking the fuel (created by vacuum) up and into the fuel pump.  Once it gets to the fuel pump, the pump then pumps (using pressure created by the 2 cycle sucking of the crankcase) pushing the fuel into the carburetor.


Second I would say, look closely at all the fuel line connectors, are they snapped onto the tank and motor correctly?  If not, it can give you headaches.  As said above, on any no start repair, LOOK HERE FIRST.  The quick fuel connectors are a necessity now days because of the 6 gallon fuel tanks,  but they can either have a leaky internal O-Ring OR could have become slightly unsnapped, but still held somewhat in place where to the casual untrained eye may look as if they are connected correctly.  If this is the case, the motor may suck air into the fuel system, even to the point the motor will die.  This can also be seen where a auxiliary motor is ran off the same main fuel tank.  If the auxiliary motor is not being used and the coupler becomes loose/uncoupled, your main motor may die  because it is sucking air in from that auxiliary motor open coupler, if the main motor is what is being ran at that time.


On a cold start the recommended method is to pull the choke all the way out and crank it over it until it starts, within a few seconds it may sputter or may even die, push the choke in about 1/2 way and give it another pull and it SHOULD run.  However you may have adjust the throttle to about 1/2 way after about a minute and then all the way in, it should run all day.  Each motor has it's own quirks.   On a warm start there should be no need to use the choke as you may flood many motors and if this happens it will not start until you have let it set for 1/2 hour or so allowing this excess fuel to evaporate.


If the motor has sat for a while and just pumping the fuel primer bulb does not get the motor at least sputtering after you have concluded that the electronics are OK, have a squirt oil can with the proper gas to oil mix, try to start it by squirting fuel into the air intake of the carburetor as you pull the manual starter rope.   Starting fluid will work, but don't overdo it as this has no lubrication qualities which could damage the motor if used extensively.  A squirt or 2 of starting fluid into the air intake is plenty.   It is better to use a plastic pump lever bottle with gasoline mix in it.


Before we get to involved here, maybe we should consider the fuel and type of fuel being used.  The OMC service manual from 1979 states that any fuel that is designed to be used in an automobile can be used for these motors.  In recent years with the advent of unleaded fuel it is preferred, and NON-ETHANOL is highly preferred.  Their recommended minimum octane rating is 86, up to 91.   Now we are encountering the E10 or 10% alcohol.  This was never even thought of at the time these motors were designed.  From what is being pushed now for marine usage it is not good for the older fuel lines, it even loosens gunked up fuel tank debris, creates problems inside the carburetors, plus absorbing moisture from the marine air into the fuel tanks.   NOT GOOD.   And any old stale fuel would also not be recommended.


First to check would be is the fuel fresh and clean?  If the tank could have sat outside or in a boat in the weather, there could be some leakage around the cap, or gauge where water may have snuck in.  If any water is in with the gas, you will NOT have a smooth running motor, maybe even could not keep it running if you got it started as water intrusion in the carburetor will not flow through the carburetor jets.  Now if you tried to start it with contaminated fuel, you have that bad fuel inside the carburetor, which will need to be torn apart and cleaned.  It you live in a area where fuel contamination can be a problem, it may be best to install a water separator filter system in the fuel line.


The primer bulb is a manual fuel pump of sorts.  It's purpose is to pressurize the fuel system and once the motor starts, the motor takes over using pressure, alternating vacuum inside the block to activate the fuel pump, sucking fuel from the tank.  When you operate the primer bulb (or manual fuel pump) when the carburetor fills with fuel, it should start.  The fuel pump starts doing it's job once motor starts.  The fuel pump does not come into play after the starting.   If you get a gurgling noise the primer bulb as you are squeezing, it is usually not functioning right.  There are two spring loaded check valves in this bulb, one one each end, where the one closest to the tank stops the fuel from flowing back into the tank, while the one toward the motor retains what is in the bulb until you squeeze it again.  A spring could have become broken or dislodged, breaking the chain of the bulb sucking from the tank and then pushing to to the motor.


With the motor running your bulb is no more than a fat piece of fuel hose so you can expect it to become soft at that point.  After the motor has run enough to remove this pressure of the internal fuel you have pumped, the bulb should become soft as the fuel flows thru it.   If primer bulb NEVER gets hard, you could have a air leak in the fuel line up to the fuel pump, it is possible that the fuel is shooting into the crankcase, or the carburetor float needle is not seating, but if this is the case then fuel should be leaking out of the carburetor.


Some motors will have a fuel primer system instead of a choke.  The incoming main line goes as before, directly to the carburetor, some have a Teed line to the primer.  Others (later ones), the main fuel line goes directly to the carburetor and then a separate line from the bottom of the carburetor bowl goes to the primer.  From the primer body, another line goes into the carburetor throat, or into the intake manifold, bypassing the carburetor.  These primers usually have 3 positions, (1) In, is that it is inactive, (2) All the way out it squirts a small amount of fuel into the carburetor, or manifold to prime the motor.  (3) But when pushed to the mid-position it acts as an enrichening valve for cold starts, letting a little fuel in, to keep the motor running until it warms enough to where you can push it all the way IN (kind of like partially choking it) so the motor can run smoothly without any assistance. 

These primer systems are basically a plunger type pump and may need attention over time as
internally there are Neoprene O-Rings that act as seals on the piston, which can deteriorate.  If this happens, you may have an engine that may start with persuasion, but  may not remain running OR dies as you open the throttle up.  What is happening is that the motor is sucking air around the leaky O-Rings and not getting enough fuel.


Second to check would be to whether fuel is coming to the motor.  Is the fuel line connected to a VENTED tank.   It works best if you hold the primer bulb upright, with the outlet upward when pumping it.  If the check valve spring is weak, this will help the pumping by not allowing the fuel to bypass and go back into the tank.  The primer bulb should become hard after about 3 or 4 pumps when the carburetor bowl becomes full, the float valve stops the fuel from bypassing, going in to the carburetor float bowl.  If the float valve does not close and you keep pumping, you are forcing fuel up into the carburetor body, flooding the motor.   A simple way to check if it the tank, pump bulb and line is functioning is to use a nail to push in the small metal ball on the motor end of the fuel line coupler.   While you are holding this ball in, pump the primer bulb.  If fuel gushes out this coupler and all over your hand, everything is OK up to there.  


Also if you are using a LONG fuel line because you need to place the fuel tank farther away that the normal 6' hose, this may cause problems if the fuel pump is not operating at full efficiency or there is a air leak in one of the fuel line fittings.  This may also be a problem even if a standard length fuel line is being used, if you are trying to start the motor in a barrel where the fuel tank is setting considerably below the motor.


A faulty fuel pump would not stop it from starting IF you pumped the fuel line primer bulb up and filled the carburetor float bowl.  If everything else is OK and the carburetor bowl is filled by pumping the primer bulb, the motor will start, it then won't stay running more than a few minutes because the fuel in the bowl is used up if the fuel pump is bad.  Repeated bulb pumping can keep the motor running if the fuel pump is inoperative.


Fuel Filter :  When they went to the new style fuel pump (depending on the model) in 1968, this pump included a fuel filter (of sorts).   As seen in the photo below the black plastic inlet is secured by a single center screw.  By removing this screw, this inlet cover can be removed, UNDER and pressed into the underside is a fine stainless steel filter screen.


If you are working on an earlier motor, there may be a glass sediment filter bowl under the carburetor.


Here is the later style fuel pump showing the combo filter/inlet on a 9.5 hp



If the motor still fails to start and the suspect could be fuel, I would then replace the 3/16" fuel line from the fuel pump to the carburetor with a clear see thru line.  You will be able to see fuel in this new line when you pump the fuel line bulb.   This will give you an idea if the fuel pump is functioning.  Matter of fact if I get any motor that appears to have a fuel problem, the first thing I do is replace this line with a clear see thru one.  It has saved me lots of time trying to run down fuel related problems.  However do not expect a complete fuel full flow to the carburetor, as you will get it in spurts because the fuel pump is being activated by being connected directly to the crankcase which uses vacuum inside the crankcase when the piston moves in and out, so you may get a few bubbles showing in this clear line.


Have you removed the and cleaned the carburetor completely?   If you frequent the outboard motor repair forums, the assumedly cure all for motors that do not run right if they have been setting for a year or so, is to tear it apart, clean/reassemble.  This may not be the cure all, but it sure does not hurt to be sure the carburetor is free of rust and debris.  Normally if you are going to let the motor set for some time, you should run the motor enough after you disconnect the fuel line from the motor to where it uses all the fuel in the carburetor and dies.  This then pretty well assures that the picture shown below does not happen.  The one thing you do not know when you purchase gasoline, is just how free of water is it?  Most all of the larger boats use a water separator filter system.  But unless you live in an area where the fuel is known to be contaminated, these separators are hardly ever used in conjunction with small motors of the size we are covering here.


If there is any water in the bowl, it will usually block the main-jet and stop the motor from starting or at least make it run erratically.  Rust will also do the same thing by blocking or partially blocking the jets.   Now if there is water in the fuel of the carburetor that has not been drained, the result can look like the picture below.  You will note that on the newer motors, OMC did away with the metal bottom and replaced it with a form of plastic/nylon, which would eliminate this rust kind of problem.  However you could still have the water problem.


Rust in this old metal carburetor bowl, not a good thing, it is understandable why they went to plastic bowls.  


(3 1/2) Motor Won't Run Unless You Pull The Choke  :

A backyard mechanic's approach to this (if it has access to the mouth of the carburetor with the breather/airbox off) is.  Rev it up and choke it with your hand to create a high vacuum.   Sometimes this will be enough to pull the jelly sludge thru the carburetor.  If this does not do the trick, then pull the idle adjust fuel screw out after you count the turns in so you can replace it to it's original setting.   Spray carb cleaner, or aerosol Sea Foam in the hole to clean it, let it set for 1/2 hour, screw the needle back in until it lightly bottoms out and count the number of turns out that it was set at originally.  Start it up, and rev it up trying to pull any gunk thru the carburetor.   If it is still not operating right, then your only option is to rebuild the carburetor, or at least tear it apart and clean it.   Be sure to start with clean gas can and lines.


The 1994  9.9hp motor that was my trolling motor for 3 years when I bought a newer Yamaha T8 with power tilt, this older one sat in the corner waiting for a friend to come up with the money to buy it.  Never happened and when I later tried to start it, the carburetor float valve was stuck open, allowing fuel to be pumped into the carburetor and out the vent hole in the upper section.  When tearing it apart, I found greenish moss encompassing this needle, also the same greenish film in the float bowl and on all brass tubes inside the carburetor.  Time for a soaking in carburetor cleaner.  I must not have ran it dry on the last run, but there was a film still inside.


If you do not know any history of the motor, then it may be best to suspect the worst.  Do not purchase a can of spray carburetor cleaner, thinking that you can spray it into the breather while the motor is running and consider the carburetor clean.  Doesn't happen that way.  It may look like a diamond on the outside but like a sewer on the inside.


Usually you can tear the carburetor apart, clean it up, blow out as much as you can with compressed air and a simple reassemble with good results.  However most of these older metal topped carburetors have one or more small soft plugs that plug a hole that was drilled in the body to make air or fuel passages.  If you blow everything out with air and the motor still doesn't want to fire or run properly, just maybe there is a blockage in these holes under a soft plug.   The newer plastic topped carburetors do not have capped off channels as the diversion of air or fuel is controlled by the gasket between the carb body and the plastic top.   They make different gaskets whereby one body may be used for different motors.


However if you do tear one apart, when you reinstall the bowl float which has the inlet needle attached, check the float setting, which with the  float installed (bottom bowl off) and the unit upside down the float resting on the shut-off needle, this float needs to be parallel to the carburetor's body.  Most of the newer carbs will utilize a small spring clip attached to the needle which pulls the needle open when the float drops allowing new gas to enter.  The older floats did not use this spring clip.  One suggestion is in reassembling these to hold the unit (with float installed) and blow into the carb's intake fuel line.  No air should pass thru, continue blowing and lift the float.  Air should bow through.  Basically you are checking the operation of this fuel shut off needle, otherwise if it doesn't work, you will not know until you have it all together and will need to tear it off AGAIN.  If it is stuck OPEN, you will not be able to pump up the fuel primer bulb making it hard AND lots of fuel will be running out the front of the carburetor.  On the other hand if it is stuck CLOSED, no fuel will get into the carb.


I once ran into one motor that apparently had a watery grave, possibly during a flood because inside the carburetor, the main jet and the main jet passage tube were both plugged with a VERY FINE silt.   I was able to remove the main jet, drill out the plug using the same size drill as the jet was made originally for.   But then after having this carburetor off more times than I wish to remember, it finally hit me that possibly there was a blockage in the main jet tube under this soft plug (the only place I could not see thru).   The price of a new soft plug was only $3.42 where the complete carburetor kit a mere $43.40.  I ordered a new soft plug.   But with fishing season approaching before it came, I removed the old soft plug by driving an ice pick into it then prying it out.   Sure enough, the tube was plugged almost solid as the main jet had been.    On this model the tube had a slotted end down in the carburetor's body, indicating it may have been threaded in.   However in trying to unscrew it, it soon became evident that I would ruin it before it came loose.   So I straightened it best I could, blew the tube out with high pressure compressed air.   Now I can even see thru it.  I then peened the old soft plug slightly, reinstalled it, placed some JB Weld epoxy over the hole that I had made with the ice pick.  It ran so well that I never put the new soft plug in.


Before this it would have been totally impossible for fuel to get from the float bowl into the motor, that is why it would sputter when I squirted fuel into the choke area.  And the previous e-Bay seller said he had just ran it the week before.


Another thing to look at is if you are running 2 motors off the same main tank, like say a 150 hp and a 10hp in all probability the large motor's fuel pump may well pull the fuel out of the small motors fuel line if the smaller motor is not running.  Now when you try to start the small motor you have to pump the priming bulb for some time as your fuel line may be empty, and you will need to bring fuel from the main tank through that fuel line and into the carburetor.  In this case, you need to install a anti-siphon check valve in the fuel line at the tank for the small motor.  These are an economical small in-line check valve units that have a threaded fitting on one end, have a hose barb on the other end.   Measure your fuel line so you can buy the right size check valve.  You probably do not need to place one in each fuel line as the smaller motor's fuel pump should not be powerful enough to drain the other line. 


Also consider if there may be a slight air leak in the fuel line and the motor has sat for a while where the fuel may have partially drained back into the tank.  When you try to pump up the smaller motor's primer bulb, you pump till you get tired and it still does not pump up.  You may have an airlock at the pump where the only way to get it out is while you are pumping, push in on the ball at the motor's end, relieving the internal air, allowing the fuel to be hand pumped enough to fill the line, removing all the air bubbles.  One suggestion here is to use a nail or something pushed in holding the ball down, while holding this line end high in the air when pumping, allowing all the air to escape.   Then remove the nail, the line should be pretty full.


If the preceding tests do not allow the motor to start, then check the vent on your your fuel tank's cap.  If you are using the old metal OMC tank, the cap is vented by the center screw head having slots cut under the head, or through the fuel outlet on the tank when you connect the line coupler as seen in the photo below. This will automatically vent the tank unless these small notches get plugged. 


This old metal single line OMC tank has 2 SMALL spring loaded plungers protruding above the line & guide.  When the connector is coupled, these pins are pushed in allowing a small vent hole through a recess below the LH pin.


The newer OMC plastic SysteMatch tanks I have not personally inspected, but from a picture it appears that they also need to have the vent screw backed out like the aftermarket tanks.


If you are using any of the old style newer or aftermarket plastic tanks, they all require you to unscrew the vent screw slightly.  This need not be backed out to the point it may fall off, but just a part of a turn or so.  If you do not vent the tank, the fuel pump will suck a vacuum and no more fuel can be pulled into the carburetor.


As of 2012 all the new plastic aftermarket fuel tanks are required to be automatic venting.  A main  criteria is that all fuel tanks have to be vented to operate, therefore they have be vented either automatically or manually.  These new tanks have a spring loaded automatic vacuum one way venting system in the filler cap.  However one of these that I have as a spare on my larger boat where I have all the fuel lines constantly connected to a valved manifold, these new tanks act on vacuum from the motor, but do not take into account for pressure building up inside the tank in hot weather, so that quick connector from the spare tank to my manifold leaks a small amount of fuel when it the weather warms up.  The EPA says this fuel venting for the multitude of boaters out there is part of the air contamination problem.  BULL SHIT.  Now you may also see another twist to this which is Moeller is currently making a new fuel line assembly with the ends and priming bulb that has a different quick connector at the tank end.  It is toted as a cure for pressure build up when you disconnect from the motor where this new IMPROVED unit is supposed to stop any leakage here.  However it replaces the tank connector fitting, so if you have more motors than the one you are going to use this new tank on, you will have change all your tanks over OR buy the old style quick connector and replace the one on this new style tank with the older style connector.  AGAIN, MORE BULL SHIT, just like the doctors prescribing another medicine to counteract the previous one's side effects.


Check the fuel connectors to both the motor and the fuel tank.  Sometimes they may pop off just enough to disconnect themselves but still be on the guide pin.  The worst coupler to do this that I have found are the ones using a torsion spring wound around a central pin, with the tails putting pressure on the latch.  Attwood makes a fuel line coupler that uses a coil spring, which is quite a bit more secure than the torsion spring that Tempo uses.  Make sure you have the fuel line on correctly, as it can be attached either way, but the check valves in the primer bulb will only work one way.  On the bulb itself is an ARROW, indicating which way the fuel needs to flow from the tank to the motor.   Push this coupler on as far as it can go AND have the couple lock latch snapped in place.


Primer bulbs do not stay firm after an engine starts because fuel is "sucked" through them, not forced through them under pressure.   A problem can likely be due to a weak fuel pump or air leaks in the fuel line.   Pictured below is a dissected primer bulb.  The red check valve assembly is towards the tank.  These couplings/valves were dissected to show the internals.  I swapped the red with the black plastic internal valves for better picture clarity.   Normally the red will be with the red.   Both valves use the same parts but different color,  with the valve reversed in the outgoing one so that the fuel flow will go only one way.  In the suction side, (red) it has a light spring pushing against the valve to prevent fuel from being pushed back into the tank.


As mentioned before, when running, the primer bulb will NOT be hard as when you primed the motor.  The reason being when pumping the bulb to prime, you are filling the carburetor, when the carburetor float shuts off the in coming fuel, the bulb gets hard because there is no place for the fuel to now go.  When the motor is running the primer bulb really needs to be laying horizontal so the fuel passes thru with little restriction.  If it is vertical there is more of a chance for the check valves to do some slight blockage.


Dissected fuel line primer bulb


If fuel starts running out of the carburetor when you pump the bulb, then you possibly have the carburetor float stuck our the needle valve may have dirt under it and may not be shutting off when the float reaches it high position.  Also check for any possible fuel leakage at any of the fuel line fittings or at the fuel pump cover.  On the older OMC motors up until about 1990 or so that used the small fuel pump mounted on the RH side of the powerhead, there will be a large headed metal screw with a coin slot in it on the outside of the fuel pump.  This can be loosened and the cover removed, revealing a stainless steel screen.  Make sure this screen is not clogged, and that the neoprene gasket is intact and sealing properly.   Also this plastic fuel pump inlet/screen cover can get cracked.


You could also have a crack internally in the tank's pickup tube, or gummed up gas plugging the tank intake.  If it is sucking something up into or around the pickup screen the supply can be cut off, when the motor dies, this debris can fall off, the motor may start and run again for a while.  It could also be a hairline crack in the 6 gal. fuel tank pick up tube.  If the tank is full to the top no problem, but as the tank was drained and / or the outside temperature rose, the motor could die and / or surge from sucking a small amount of air.


If it runs, then dies, try pumping the bulb while it is running and see if it improves if it does then replace the fuel pump.  If it doesn't improve, then it is time to rebuild the carburetor.    Sometimes it is best to rebuild the carburetor even if it is just the fuel pump.


Another thing to look for that is many times overlooked, is the neoprene O-Ring (#0334913) on the inside of the fuel line connectors.  If the fuel line connectors' O-Rings get nicked (see photo below), or leaky fuel lines from and to pump in lower cowl, they'll let air in, and you'll have to pump the bulb to keep running.   Common problem, cheap fix. 


These O-Rings are inside the connector encompassed in a inner groove right at the outer end of the stainless steel shut-off ball.  You will not be able to see how bad they are until you take it out.  Ideally a small crochet hook works best, but you can remove it with a SMALL screwdriver or ice pick.  The are usually not strictly OMC priority so you can probably pick replacements up a at an automotive store or even a well stocked hardware store, by comparing to the old size that was removed. 


They can at times be a BITCH to remove however.


The size O-Ring that I have found that works is 1/4" ID with a 7/16" OD.   If you can not find the exact same size, then opt for one that is the same OD but thicker.  You may then have to grease this before you try to couple it to the motor or tank.  These O-Rings can get nicked or scratched just enough to not seal completely and being under a vacuum, can leak air, therefore not allow fuel to be sucked to the carburetor.  This is one item that is overlooked many times in tracing down a fuel problem.  These are worth replacing because they may seal under pressure (when you pump up the bulb), but leak under suction from the fuel pump.   Cheap and easy maintenance item, and might solve help you from chasing your tail.


The O-Ring on the right is badly chewed up internally


Check ALL fuel connections for leaks or cracks in the fuel line.  I once found one that had a small crack UNDER the clamp, if you put the clamp back on exactly in the right place it would seal, but if it was slightly different location, then there was a vacuum leak on the suction side.


Also check the gasket between the fuel pump and the powerhead.  If this gasket got misplaced during a fuel pump inspection, you will have metal to metal contact, there will be a vacuum leak so the fuel pump will not function.  This gasket is thicker than most, usually about 1/8" thick.  I suspect it is so to insulate the fuel pump from the heat of the block, thereby prevent vapor lock when the motor warms up.


If you can pump the fuel line bulb when the motor hesitates, it will resume running until the carburetor goes dry again, it is a good indication that there is a problem in the fuel supply system.   You can easily check the fuel pump operation by removing the hose at the carburetor, pull the starter rope and see if gas comes out the hose while the motor is turning over.  


As an alternate to the fuel pump, you could also take an empty 1 quart oil bottle, make a fuel line adapter that fits the cap, remove the fuel line from the carburetor and using a short fuel line, connect the bottle of fuel to the carburetor inlet fitting.   To need to be sure to vent this auxiliary tank however.   Hang it above the motor so you have gravity feed which does not need a fuel pump.   This will give you some indication if the problem may be in the existing fuel system.  I have one of these made up and use it often.


The fuel pump is powered by a pulse connection to the upper cylinder on these motors.  Each time the upper piston moves back and forth, it creates a pressure/vacuum pulse for the fuel pump.   So it is a totally pneumatic pulse operating the mechanical diaphragm inside the pump, with no wires or push rods involved.   You can test the fuel pump by removing the outlet fuel line that goes from the fuel pump to the carburetor and crank over the motor to see if any fuel is pumping through/squirting out it in pulses.   If you want a better test, temporarily tee a fuel pressure gage in the pump outlet line and run the motor at various speeds.  That will not only test the pump, but detect other problems such as clogged filters, air leaks, etc.   Some of these gages are cheap and usually combined with a vacuum gage.  Teeing it into the line ahead of the pump will also detect restrictions between there and the tank (as a vacuum test).

Another method to determine if the fuel pump is bad without the engine running, unscrew the 2 pump screws from the engine and pump the primer bulb.   If ANY gas comes out of the little vacuum hole on the back of of the pump, then the diaphragm is ruptured.  In this case with a slightly damaged diaphragm, the motor may still operate, but fuel can be sucked into the cylinder through the pulse connection hole on the block and cause the upper cylinder to flood.   Sometimes under the right/wrong conditions, with this situation, the motor will start and run for a few minutes, then die.  You can pull the rope until your arm gets tired but it refuses to start.  Wait an hour and it wills start, only to repeat the process.  The spark plugs will always be wet, as the engine is flooded.


These older OMC small square type fuel pumps are rather cantankerous to repair and make them function afterwards.   The reason is that they are so delicate and invariably, you miss getting some of the springs or valves in right.  You may notice that in the parts lists, the early ones do not show a repair kit for them.  The later kits for this same small size pump will fit, it is just that the early bodies do not have the later style index tabs on them which aids in reassembly instructions in the kit.   So you can really use the new kit in the old pumps, you will need to be sure that the diaphragms go back the same as the originals were.  To be sure you get the body parts aligned back right, use a felt marking pen to mark across the the side of the pump, identifying which came from where.   If you can not find a repair kit, or diaphragm, look around for  a material so you can make your own replacement by copying off the original.  One thing that appears may work is find someone who is on a stomach feeding tube using a gravity bag.  They have to use a different bag every day and I have found that the sides of this bag is near the thickness of most of these diaphragms AND seem to be gasoline tolerant from the minimal tests that I have ran.


Also you may want to double check the fuel pump cover, as it being plastic, can become cracked which will allow a gas leakage out, when you pump the bulb and air leakage will then break the vacuum of sucking the fuel in once the motor is running, at least until the carburetor  runs dry.  Both the above are detrimental to the engine performance/running.


If the threads around the carburetor idle adjustment screw may have gotten sloppy, you can not get a true air/fuel mixture, the motor may run erratically.  On these carburetors, there is a neoprene threaded gasket in the carburetor that acts as a seal.  A repair kit has a new one, replace it when doing a repair job.   If you are not doing a repair kit job and need to get a better seal, then you could smear some HEAVY chassis grease on and around the threads.


Now just because you have fuel to carburetor and on into the engine, spark and compression is OK, there is another item in the equation that is important with that being air.  If after you have done everything but still no results, you may have an air leak at the fuel pump or carburetor gaskets or another location. 


One thing also to consider how far are you trying to draw the fuel?  Are you using the regular 5 or 6' fuel line attached to the 3 or 6 gallon portable tank, or have you lengthened the hose to 12' so as to position your tank farther forward in a smaller boat to balance your load better?  If so you may have to replace the older small diameter 5/16" or 3/8" fuel line with a smaller 1/4" line because the fuel pump may not have enough vacuum to pull this larger amount of fuel.   This could also lead to hard starting of a cold engine if the fuel line vacuum has bled off.


Another thing is to check the fuel.   Disconnect fuel line fitting from motor and take it off the fuel line, slosh your gas tank a few times and immediately pump some fuel into a glass container.   Is it milky?    Does it smell old like varnish?   Is there water or trash in the container?  If so, dump it and clean the tank good then put in fresh new mix.   Also check the screen in your fuel pump.  Clean the carburetor again. If it has a separate fuel filter, clean or replace it.  Then clean out all fuel lines in motor.


I had a reader send me his discovery.  He was working on an small older OMC motor, but found that the varnished carburetor float was so water logged that it would not function.  He carefully removed the brass clip from the cork float and Micro waved the float to see if the water would be driven out of the cork.  He was able to re-attach the brass clip to the cork, and it did the job, getting him going again.


Another item to consider has the motor just been rebuilt and this is the first attempt to start it?  If the reed valve plate gaskets are reversed, (the front one put on the rear side) the gasket itself is a lot closer to the reed valve's exposed moving end and WILL stop the valve from opening.  This in essence totally stops any fuel from getting into the engine.  (Been there-done that & was red-faced afterwards).


If you are having significant trouble getting it started the first time after a number of years of it sitting, get a 5 dollar spray can of starting fluid to give it 1 or 2 jet sprays into the breather which could help give it a boost and will not damage the motor.  If you run the motor on only starting fluid, then you could likely seize a piston as there is no lubricant in this fluid.  It's called starting fluid for a reason, its not meant to run any motor for a significant amount of time.  If you need that, then get a oil Plews can full of mixed fuel and pump fuel in that way.


About all the above is related to lack of fuel,  --- HOWEVER  you can also have too much fuel.    Listed here are parts of correspondence with Peter Wimsett.   His symptoms were that the 1979 9.9/15hp motor was slow to rev up, and would change rev's with no movement of the throttle grip.  When running and warmed up and it would die (about 10 minutes of running in a barrel).   After a long time it would restart, giving the thought that a coil may be going bad.   All the electrical components checked out OK or changed and he even changed the carburetor.  However the final give away was the large amount of black fuel/oil coming out of the exhaust housing, first he assumed it had been running on one cylinder and it was just unburned fuel.   In hindsight the fuel pump probably had a hole in the diaphragm which actually pumped too much fuel into the crankcase at wide open throttle and which in effect flooded the engine.   He changed fuel pumps and the problem went a way.


Here is another bad fuel pump situation.  On the motor shown in the photo below, the owner had lack of power problems even after all apparent avenues (as the one above) were covered.  Compression was 120# on both cylinders, carburetor was cleaned more than once.  Fuel was mixed 50-1, but there was an excessive amount of black oil coming from the relief holes.  What was found that the fuel pump had a leak in the diaphragm and was also pumping an excessive amount of fuel directly into the crankcase, which settled into the bottom cylinder and was subsequently going out that cylinders exhaust port and then into the exhaust housing of the motor.


Fuel pump diaphragm was ruptured


 If after you have done all you can think of and you still can't get fuel to the motor, here is one that I encountered.  I was restoring a 60 year old boat, the main motor was a 65hp (new to me) and the trolling  motor a 6hp, which I had owned for a number of years and it ran like a top.  BUT, I had loaned it out and when got it back did not do anything but hung it on the wall.  The fuel tank for the main motor was a 6 gallon plastic tank with an aftermarket 90 degree male Quick Disconnect plug.


The 6hp tank was a 4 1/2 gallon metal tank that I had resurrected by removing lots of internal rust and installed a new metal pickup tube and an identical male QD plug as the main tank that.


The main motor ran fine off it's tank, but the trolling motor's primer bulb would not even pump up solid.  I swapped the connector from the trolling motor to the main motor's tank.  It pumped up, so I reconnected the hose to the trolling motor.  It ran for only a few minutes and died, sucking the primer bulb flat. 


I had made up the trolling motor's fuel line from all new parts, so that should not have been an issue.  I even changed to another new primer bulb. 


There had to be a something plugged in the small tank pickup tube.  Maybe in my soldering it together trying to maintain the screen on the lower suction end, I may have partly plugged this suction tube.  OK, I sawed it into, and checked by drill bits, to insure both sides were clear, and welded it back.


Still did not cure the problem.   And the main motor ran using the smaller tank.


Finally on a whim, I swapped both QD end couplers on the trolling motor's fuel line.   BINGO, it now was working fine.  The only thing that I can think of is that since these QD couplers use a needle type plunger that disengages a check valve  in the male coupler, that there must have been slight incompatibility between one on this fuel line, Manufacturer's Tolerances caught up with themselves.


In the photos below, you see the older style QD coupler on the Left and the newer style on the Right.   Both have dual pins, but the upper on both is simply a guide and the groove is where the lock snaps into to retain it on the tank or motor.  Notice the newer style uses a needle pin type plunger which activates a check valve.  The older style is reversed in that the ball in the coupler is the check valve and is released when the couplers are fully mated.

They are designed to be compatible with each other.   


On this older fuel tank QD coupler, it has no detent pin On this newer fuel tank QD coupler, it has a pin plunger detent



(3 3/4) Motor Won't Idle : Here, in all probability it is in the carburetor.   The first and easiest thing to look at is the idle adjustment needle, they normally are about 1 1/2 revolutions out from a lightly bottomed out position.  If you can not get it to idle by moving this needle either way, then remove it and look for wear or a bend on the needle's tapered end.  If that looks good, then where this needle is screwed into the carburetor, is a packing gland that is designed to be tightened against the needle's shaft sealing out any chance of sucking air into the system.  Or someone may have removed the carburetor at one time and did not replace the gasket between it and the manifold, or the old gasket got torn when the carburetor was removed and no Permetex was applied, creating a air leak there.


If that does not do it, then a COMPLETE carburetor rebuild may be in order.   AGAIN, just squirting carburetor cleaner into the throat does not do it.  The carb has to be torn down and if it is the older ones that use aluminum soft plugs and lead shot to plug/cover the openings needed to drill air passages, these need to be removed, the carb soaked in cleaner, it all blown out with compressed air and the plugs replaced.  


Then reassemble, and go back to the idle adjustment. 


Another unusual, but possibility, would be just the opposite, in the fact that the fuel pump has a pin hole in the diaphragm, flooding fuel into a cylinder.


(4) Water Cooling System : The bulk of outboard motors were/are water cooled, requiring some sort of a water pump system.  Some were air cooled, but still needed water to cool the exhaust housing, keeping it from burning the paint.  The water intake may be located in numerous different locations in the lower unit depending on the manufacturer.  Many motors made prior to the 1960s utilized a screened water intake BEHIND the prop, using it's motion to force water up into the water pump.  This was well known in those days and the mechanics put the motor in a tank (WITH THE PROP ON) to do a test.  Now after 50 years, there seems to be many Do It Yourselfers who are new to outboards and do not understand this system, who put the motor in a small garbage can, but take the prop off so it will not cut the can.  This may allow your motor to run, but not for an extensive amount of time because of the now underwater exhaust bubbling in the can, which disrupts any water flow (because of a lot of air bubbles) up into the pump.

If there was an aftermarket water intake attachment, they are now long extinct, so use a large enough barrel, or attach it to the boat and put it in the water for a test.

If you can not achieve a high RPM in a barrel, (with the prop on) this can sometimes be attributed to the engine smoking badly in a barrel which is essentially so much smoke (exhaust fumes) that the motor in the confined area of a test barrel that the motor is trying to re-breathe the exhaust, which has little oxygen left in it now.  To test for this, remove the top cowling motor and see if that helps.

Another situation that you may run into is that if you decarb your motor and then run it in the test barrel, you WILL have a lot of smoke.  This would probably be worse than just a lot of exhaust smoke.   Put an electric fan near and see if that helps.

Also the cooling system has to have water flowing through it.  This could be restricted at the intake, as mentioned above, or in side the motor, especially if it has been used extensively in saltwater.  Or used occasionally in salt water and not flushed, then sat for some time, allowing salt crystals to build up and block passages.  So first off, if the motor is getting warm or not exiting exhaust water, it may be beneficial to check/replace the water pump impeller.  If you still get the suspicion that there is still no/or minimal water flow, look deeper.  First would be check the thermostat, these are usually rather simple to get to in relationship to other repairs as the thermostats are a thing that needs attention quite often.  They will usually be in a cavity in the head/motor and covered by a bolt on plate.  Pull them out and carefully clean if there is any debris covering/in them.  If they are coated with salt crustation, sometimes a soaking in ordinary Vinegar will loosen that.  Once clean, to check if it is functioning properly, place it in a pan of water and bring it up to a boil.  Most of these are designed to open at from 145 to 165 degrees.  I fit is stuck, then time to purchase and install a new one.

If all that does not help, then pull the head off and check/clean any debris out of the water jacket cavities around the cylinders and inside the head.  Most small outboards do not have rubber grommets at the juncture of the intake /outlet water tubes, (except the 9.9/15hp OMCs which can deteriorate and plug water passage).  Most all of these smaller motors have a water jacket cover on one side of the motor, if so pull it off and again clean any passages.

If your motor is old enough and does not have a tell tale pee tube (overboard water indicator), I suggest that you install one so you can see the actual stream of water.  This is not all of the water, but only a portion of it.


(5) Hard Starting When Cold : This may sound stupid, but have you actually pumped the fuel line primer bulb until it becomes hard, thereby pumping fuel into the carburetor?   I know two boaters who always complained that their motors were hard starting, but they never pumped the primer bulb.  One said someone told him that you should not have to.  Yah, be sure to listen you those barstool mechanics.  If you just start pulling the starter rope, you will have to pull it MANY times for a motor that has sat for some time to suck enough fuel into the carburetor to get it to start.  That is what those rubber fuel primer bulbs in the fuel line are for. Also we are assuming that you have already read and applied #2 pertaining to fuel in this article.


Another very likely possibility is that the twist grip throttle is not rotated far enough to the high speed side to pull fuel from the carburetor into the engine.  This is covered extensively above.


Some motors are finicky in that they may only require the choke be fully closed (knob all the way out) for possibly 2 pulls of the rope, then it be placed in the 1/2 way open position for other pulls, otherwise the motor may be flooded.   Once it becomes flooded there is so much fuel in the cylinders and spark plugs are soaked that it may need to set for a while, or the rope pulled REPEATEDLY with the choke all the way IN to get it to finally fire.   Possibly you may even pull the spark plugs, clean or replace them.  So you may have to get to know your motor's starting needs.


Or if you have a post 87 motor 9.9 or 15hp OMC, the cable linkage may be out of adjustment.   This can be that the plastic ball coupler end on the cable needs to be screwed either in or out to be more compatible with the stators position.  There is also a plastic threaded sleeve on the end of the cable sheathing that screws into the lower cowling pan, that may need adjustment.


The one most common problem with hard cold starting, if the motor is in reasonably good running condition, can probably be contributed to someone unfamiliar with motors, who just gets into the boat, pulls the starter rope and goes fishing.   And the carburetor idle adjustments are not set for running but usually set more for trolling.


In actual use with the motor strictly set for lake trolling the fisherman is prone to adjust the idle jet lower than it is actually designed for.  When you are adjusting this timing and idle jet for slow trolling, you will be doing so while the motor is warm and running.  Then when the motor cools down, things are going to be slightly different.  What happens then is that in the cold starting mode, the motor does not get enough fuel, you have to choke it, pull more times on the starter rope to get enough fuel into the cylinders for it to fire.  One thing you may do in this case is to after you have adjusted it for your trolling speed is to then pull the knob straight forward and off the carburetor idle shaft, reposition the idle knob to position the pointer straight down then push it back on.  Then when you go to start it, you twist this knob counterclockwise all the way up (about 90 degrees) till it bumps.  This should give you more fuel to start, then you can reset it to your known trolling position later.


Getting into a worse case engine scenario which would require a rebuild, you may have worn piston skirts.  If the skirts are wore or there are horizontal score marks in the cylinder, it will not help pull fuel in when cold.  Here you can have somewhat good compression but the engine has no vacuum to pull the fuel in.   A warm piston expands some and makes a better seal on the skirt.  You can usually get it to start by squirting fuel into the right side of the air intake (breather) to get it to start, after it runs a while the metal may warm up, expand, possibly could be easier to start when then warm.  Compression is related here, but does not relate totally because the rings are designed to seal from the top side of the piston.   Compression could be acceptable but still not related as you are comparing vacuum on the carburetor side to piston compression on the head side.  The reed valves could produce the exact same situation if they are bad and not seating completely.


Another problem could be leaky reed valves at the reed valve base.    This could allow some of the intake fuel to be pushed back out on a firing cycle.  Or someone installed the intake manifold gaskets in wrong, holding some of the reeds closed, starving the motor and if ran for any length of time could create to a starved dry cylinder resulting in a seized, blown piston.


Another possibility is that the engine may have worn/leaking crankshaft seals.  This condition will not allow sufficient vacuum on the intake stroke to pull fuel from and thru the carburetor.  This is usually the top seal that is bad.  Some mechanics will tell you that it is the bottom crankshaft seal, I say not really as the lower one will not have as much side pressure on it as the top seal being near the heavy rotating flywheel as the top bearing may also be worn.  This is discussed  in more depth later in this article.


Recently while talking to a couple of duck hunters who experienced a OMC 15 hp  THAT REFUSED TO START in freezing weather.  They mentioned that one COLD morning, they were not able to go out to the hunting grounds because of the non-starting motor and they were on a trip a considerable distance from home.  A trip of "let your fingers do the walking" thru the phone book took them to a old outboard mechanic that was operating out of his home based shop.  When they explained the problem, he said "OK I know what it is".  When they looked him up, he retrieved a propane torch, heated the spark plugs.  After reinstalling them, BINGO, the motor started.  His explanation was that on some of these older motors the compression may be lower during the cold weather and that there just is not enough compression to fire the fuel at the plugs with them being that cold. 

(6)   Compression :  Pull both spark plugs and check the compression.   A good compression reading for a used 9.9/15hp motor will be around 90 PSI.   The lowest compression I would like to see and have them still run OK would be above about 60# + PSI.   Now be advised that these rope start motors do not spin the motor over real fast so the compression will be less than if you try it with a electric start motor.  There may be about a 15# difference between rope and electric start motor.   For a rope start motor, you need to pull the rope as if you were mad at it, not those love pat pulls.  You may get a higher reading if instead you use a rope wrapped around the flywheel (more purchase on the outer rim and no gear reduction).  


Use a good screw in type automotive compression tester.  You may encounter slightly different readings even when using 2 different testers, even if they are the same make and model.  Twist the throttle handle to wide open to open the throttle plate to give it as much a chance as possible to breathe and allow optimum suction.   Ground out both the plugs so as to not damage the electronics of the CDI ignition, or leave your spark tester hooked up.  Pull it over aggressively as if you were trying to start it.   You may get a difference of opinion here, but 3 pulls seems to be the norm for this test.  Pulling it more than that does not give you a fair evaluation because just because it pumps up higher shows nothing in relationship to the actual compression needed for starting.  Do both cylinders with equableness in effort as to speed of your pulling and the length of the pull to assure that you are getting genuine readings.  I like to pull it just far enough that I can feel the starter rope bottom out at the end of the stroke, but not enough to overstress the rope.


Regular automotive compression tester


You will not find a factory recommended compression data from OMC, but they will say it needs to be about equal between the 2 cylinders, this being within about 5# of each other.   As for compression testing, I have found that not all testers come up with the same pressure.   I have had 3 and the neighbor a different one, there is 15# difference between them.   You might just have a low reading one.   One of my gauges broke (stuck at 60#)  and when I tried to purchase a new gauge from Car Quest.   They checked with their supplier who said just a gauge was not available.   My guess is that these are made so cheaply it is not feasible to repair them.   Also what I found was the "valve seat inserts" are made in a different internal color, these colors use a different tension opening spring, (car inner tube version is overly strong in comparison) so the inserts may need to be matched with the gauge.   And since we are usually manually pulling a rope as compared to a electric starter, the pressure reading will probably be different.   I have a feeling this is why OMC has not posted a recommended PSI reading, as mechanics would be chasing their tails over a few pounds.


I have seen used motors seemingly run quite well at 75# and others that were a new rebuild at 125#.   However some motors will perform to the owner's satisfaction and requirements at only 60#.   I personally would NOT like to see anything under the 85# however for the 9.9/15hp, especially if one was at 50# while the other cylinder was at 80# or 90#.  This out of balance one would be a candidate for a decarb job, or if that doesn't help then a re-ring job as the low reading cylinder very likely has a seized ring or broken or broken ring.   It would possibly be hard to start, with one plug would more than likely foul out often.  However on some of the older motors with a gear reduction rope starter like the earlier 6 and 9.5hp motors, it seems that if you get 70# you are doing good.


I have seen some that run fairly well with a medium compression, but the rings or at least one is bad, however there will be fouled plugs or excessive smoking problems.  The consensus from many boat mechanics is that if you have compression in excess of 110# on this series of used motor, that you have an exceptional motor.


What a compression test will tell you is if one cylinder is 90# and the other is 40#, you can very likely have a blown head gasket and the lower compression cylinder compression is leaking off into the water jacket.  Or, if both are at say 70# the gasket is blown between the two cylinders and is equalizing when you take the reading.


Compression is not the only test you need to look at, but if taken into consideration with other factors it may well lead you to some conclusions as to the condition of the motor.  A compression test will not show is a secondary compression which on a 2 cycle motor the crankcase must alternate under pressure and vacuum.  After the piston closes the intake port, further downward movement causes the fuel/air mixture in the crankcase to be pressurized so it can move quickly into the cylinder when the exhaust ports are opened.  Then the upward movement of the piston creates a vacuum in the crankcase which in turn draws new fuel/air mixture in from the carburetor.  If the crankcase seals or gaskets leak, the crankcase can not hold the pressure or vacuum to operate the reed valves behind the carburetor, the engine will not run well, if at all.  This vacuum is also what operates the fuel pump.


Possible things that should be checked are, and in this order (1) cylinder head gasket  (2)  spark plug threads/gaskets  (3) carburetor mounting gasket (4) fuel pump gasket  (5) crankshaft seals (6) any crankcase joint if the motor had recently been torn apart.  The most probable is a blown or leaking head gasket.  If the gasket is blown between both cylinders it will not start, however that would be the rare situation as the leak usually is between the cylinder and the water jacket, which will allow water into that cylinder.  This could also effect the cooling of the motor as this compressed gas could be forced back into the cooling system.  A blown head gasket can lower compression enough to make the motor hard to start or not able to run at low speeds.  It will also usually be associated with that cylinder's spark plug continually being fouled.


Look at the head gasket.  Any time you have the head off, check it for straightness of the head using a straightedge.  To repair a slightly warped head, this can be done with a good file, but better by using a medium valve grinding compound on a old glass window large enough to allow the read to be moved around on it.  Smear some medium grit valve grinding compound on the glass, place the head on this, move the head around applying downward pressure while doing a figure eight with the head to take off any high spots.  Lapp the head, applying more compound and the figure eights until the texture of the head has the same wear pattern all over the bearing surface.  After it has been run enough to warm the block up, check and re-torque the headbolts.


Now don't be misled by just a somewhat high compression reading.  Look at the photos below.   Here the motor had been totally rebuilt with new rings about 30 hours before.   The standard 50-1 gas/oil mix was used.   The motor died and since it had an electric starter, was not noticed any real differences except harder starting.  Plugs were changed and it ran for a while.  This time when it died, the lower plug had the electrode smashed flat against the center electrode.  At the time it was thought that possibly the new plug was defective or that it had been dropped, deforming it.   The motor was still running with about 4 more hours on it at the time it was taken out of service, but the bottom plug was fouled considerably.


Here is the bent spark plug mentioned above


Compression on this motor at the time it was taken out of service was 108# on the top cylinder and 105# on the bottom.


Miraculously, the cylinder wall was not scored badly and only a good honing job was required to clean it up.   But the block got bulged with a hole about 1/8" was discovered on the RH #2 cylinder location just forward of the cylinder liner.  This was cracked by aluminum piston pieces being sucked behind the piston thru the ports, then got poked out as the rod came around at the base of the cylinder.   A clean up and wire-feed welding job remedied this problem.   However this hole in the block could have been probably been taken care of with a J-B Weld epoxy repair.


What amazes me is that even with the hole in the block and the broken ring/piston that this little motor still ran, not good, but it ran enough to get us back to the boat launch.


Here is evidence of the broken piston pieces being imbedded into the head Here the blown  piston, missing the top section of the  lower LH ring groove.   Note, the arrow pointing to the  top ring  groove that has broken but the ring stayed in place in the groove.


If your testing shows low compression, then I would do 2 things, before I would get really dejected.  First I would pull the head and look for a blown head gasket or evidence of carbon on the top of the piston.  If carbon is there, then you may also have it in the ring grooves binding the rings from doing a full expansion contact with the cylinder walls.  This could seize the ring to the piston groove and cause it to not seal in the bore effectively, which can contribute to low compression.  While the head is off, rotate the flywheel, look at the cylinder walls, are they scored or evidence of rust pitting?   One thing to do when taking the head off, would be to mark which coil is the top one (this will be an invaluable help later).    Another thing to remember for the pre 1993  9.9 and 15hp motors is that when you took the head off the 2 bottom bolts could not be taken out of the head while it was still in place because they hit the lower cowling.  This means when you reinstall the head IF the powerhead is still on the motor, that you will have to insert these 2 bolts in their respective head holes BEFORE you slide the head in place.


The next step would be to remove the bypass cover on the LH side of the motor facing forward.  With this cover off, you can see into the side of the powerhead, see the sides of parts of the piston and the rings, which will give you another clue as to what may be wrong.   Is there any black carbon on the sides of the piston, which would indicate that the rings are indeed stuck allowing a blow-by.  Check to see if the rings are stuck in the ring grooves, or is the piston grooves worn enough so that the rings wobble in the groove?


       Rusty/Carboned cylinders, 62# & 105# compression, not good.

Bypass cover removed showing pistons & rings thru holes, note top piston evidence of rust/corrosion ON piston  Bypass cover removed showing scored pistons & very likely cylinders also, indicating  possible seized or broken rings

The white color in the water  jacket around the cylinders, top & bottom is salt deposit.

Note rust, especially for the bottom cylinder.  This motor had blown head gasket on lower cylinder This motor was smoking excessively & using lots of gas


Since these motors are 2 cycle, and fire on the rise of the piston each time, it is crucial that the motor has GOOD compression on each stroke.  You might therefore compare the compression on the first stroke, then against cranking it over another 3 or 4 times.  By the nature of most compression testers, they allow a compounded poundage if cranked repeatedly.  Just because you can come up with a higher compression by cranking it over more times, does not give you a true idea of the 2 stroke motor's capabilities and needs.


If the motor runs, but just doesn't seem to have the power and you have checked every thing else, try re-tightening the head bolts as you could have slight compression leakage.  If this leakage has been there for a while and blown a hole, it will then need a new head gasket.


Be sure you get the right head gasket, as the ones made for the post 92 models do not fit the 92 and older models.


I have been communicating with one motor owner who is having lots of smoke coming from his motor when trolling where it uses LOTS of fuel, he says like an old V8 Ford.  He has had it to mechanics but no one had narrowed down his problem.  They are looking at leaks in his exhaust system for the smoke.  His compression is 90 and 95#, the plugs are very oily but he has not had them foul to where the motor dies.   My thoughts were that he has frozen rings in the pistons, or rings that have lost much of their tension so he is getting blow by.   He later sent me the picture on the right above.

You would be amazed at how these motors can run at times while needing major internal repairs.   Kind of like the Energizer Bunny.


(6 1/2) Compression Bypassing Rings :   I have heard of one guy was having idle problems and also fuel dripping out the carburetor, who thinking maybe the fuel pump wasn't getting pulsed by the motor pressure/vacuum changes, he removed the fuel pump, held his thumb over the fuel pump hole on the power head to see if he could feel any pulses and started the motor.  When he pulled his thumb off the hole, fire shot out that hole and toasted the end of his thumb!  Not a bad burn, but just enough to get his attention.


My guess is that his rings are not sealing good enough to not allowing enough vacuum to pull the fuel into the crankcase, (possibly a source of the fuel leak also) also evidenced by fire coming out the crankcase fuel pump hole (also bypassing the rings).  Maybe a time to decarb the engine and hope it will loosen the stuck rings, other than that, a re-ring job would be in the future.


(6 3/4) Bad Head-gasket : A slightly defective head gasket can cause engine heating at high speed and cooling off at low speeds. What is happening is with a slight leak, at higher RPMs may be pushing compressed fuel into the water jacket, disrupting the water cooling flow, when the RPM drops so does the percentage of bypass, whereby the motor's cooling water flow is back closer to normal.


(6 7/8) Time to Re-Ring :  A time can come when no matter what you go, the motor just is getting tired and will need to be torn down and the rings replaced on the piston.

OK, we have covered the main items to look at.  The following areas may be additional add on's of the above if you are still having problems.

(7) Flywheel Key Sheared :   Another check would be the flywheel woodruff (1/2 round) key as mentioned previously.  If for some reason, the flywheel nut was not totally tight, and/or the motor had backfired, or the motor was stopped suddenly, (like hitting an object) the flywheel key could have gotten partly sheared off.  If this happens, the flywheel can get slid (rotated by centrifugal force) enough to throw the timing magnets off enough to create hard starting or possibly not allow it to even start.   If the flywheel was not really tight when the key may get sheared off, it is possible that the flywheel would rotate without the crankshaft moving.  If this happens then it is also possible that the manual or even electric starter spin but would not rotate the crankshaft because it was simply spinning the flywheel on the shaft.


You may see different opinions as to how the key needs to be inserted into the flywheel cut.  Probably it really makes no significant difference on a used key, but for a new key there may be some benefits.   I have found a illustration in a newer OMC service manual that shows the key inserted with the punch mark down, as shown in the photos below.    There is another diamond or triangle (depending on manufacture date) punch mark in the mid center.   I suspect this is their way of trying to compensate for any wear in the flywheel slot and are forcing the flywheel and crankshaft to be tighter if used in a motor that has a worn slots and a new key.   There was never any marks on the old keys.  I guess this is why the new engineers are paid a higher wage.   In this manual they stress that the outside of the key be parallel to the center of the shaft. 


I ran into one motor, a 1974 that repeatedly sheared flywheel keys.  After 3 of these, I finally wised up somewhat, and did some investigating.  This motor did not have the original powerhead, so the flywheel tapered hole was not an exact mate to the crankshaft taper.  In this I found that the flywheel on the original motor may have been loose at a time, allowed slight wear in the flywheel's tapered hole.  Since these are tapers and the flywheel has to slide far enough down onto the crankshaft taper to become a tight fit, this flywheel taper had become slightly oversize up to within 1/8" of the top where it was still the original smaller size. 


What was happening was that with mismatching parts, the flywheel slightly smaller upper size was hitting the top edge of the crankshaft taper, not allowing this different flywheel to be tightened down enough by just tightening the nut.  A large round chainsaw file was used to remove this ridge in the upper flywheel tapered hole, then in assembly the flywheel was hammered down with a brass mallet, then the nut was tightened.  However this created another problem of the flywheel now being lowered just enough to rub the timing plate, creating excessive resistance when twisting the twist grip throttle.  If you have access to a large metal lathe, you could mount the flywheel in the chuck and remove a slight amount of metal on the underside where it was rubbing, OR find a used flywheel of the same vintage.


Shown in the photos below is a new flywheel key which has some punched marks on one side, this particular one fits the 1974 thru 1992 motors OMC #318931.   The markings on one side of the keys have a meaning, and all I can find is they go in pointing down.  These markings should have the some meaning, so with it indicating the small edge mark is down.  That probably is to ensure it is tight in the slot as the flywheel is lowered into place.  The other upset mark in the center is probably to also swell into the slot making sure it is tight if a worn slot.

However in the RH photo below, in the 1974 service manual the key is supposed to be parallel WITH the taper of the shaft, someone goofed in this drawing. 


The OMC 1993 and newer 2 cycle, plus all the 4 cycle motors use a different wider key, part # 307480.  The older key sells for just over $5.00, while the newer one is at $3.00, telling me that the cheaper key is not made by the factory but is a standard key off the shelf of a industrial supply.


Note the 2 punch marks on the side of this new flywheel key Illustration out of an OMC manual

(8) Advise When Flywheel is Removed :  Any time you remove the flywheel, and lay it upside down on your workbench.  If you don't inspect it completely when you get ready to reinstall, there is a very great chance that one of the magnets may pick up a piece of metal or a nut, that you may not see when you reinstall the flywheel.  I had this happen one time after a rebuild and the flywheel drug on the timing plate badly.  What had happened was that this motor had sheared a flywheel key and the thin outer part had been held in a inconspiculess location by one of the magnets.  Somehow later during running the motor, this thin outer part of the key loosened up on one end and during the motor running at a higher speed one end swung away from the magnet and inward, catching the condenser and charge coil damaging them.


(9) Throttle Position/Timing :  This may not be as critical as the others, but worthwhile to check, since it is not in open view, it can slide by un-noticed.  The twist grip does have a position marked as "START".  This is a position where the timing plate's cam positions the carburetor arm to where the ideal setting is for starting in relationship to the flywheel magnets and points or CDI sensors.  This cam plate setting should not normally have to be reset unless someone has tinkered with the motor, they unknowingly may have changed this setting.


If the twist grip is not rotated to a fast (advanced) enough position, you will have to crank all day on a cold motor, however if you advance the grip to a FAST position, it will start readily.  You may have to quickly readjust the throttle to a more medium speed once it gets to running.

The throttle cam plate operates a cam roller that is attached to the carburetor.  If this cam roller is cracked, broken or not functioning, it will throw the timing off.  The throttle cam plate also rotates under the flywheel when you twist the twist grip. This cam plate has an arrow type mark on the front of it.  This mark needs to be timed so that when you advance the throttle twist grip, that the carburetor roller is at this mark when the carburetor throttle shaft just starts to turn open. To adjust this on the earlier motors, you need the flywheel off, loosen the 2 bolts on the RH side of the plate, adjust the cam plate to where it just aligns with the roller. To tell exactly when the shaft STARTS to move, take a small alligator clip, attach a 2" wire to the wire end of it.  Clamp the clip onto the carburetor throttle shaft's Starboard side with the wire pointing UP.  Twist the throttle until you see this wire pointer just move.  The cam plate arrow should now be lined up.  If not, loosen the 2 screws on the side, rotate the plate cam until it is aligned and retighten the screws.

Some mechanics like to set them so that the throttle arm JUST opens up a bit when this full neutral throttle is applied, I am inclined to agree.

On the later OMC motors the adjustment is different, (about 1986 or so) the timing cam plate that the carburetor roller engages is made of plastic with an adjustment screw on the rear (LH side) for fine tuning. The nature of this is that it is attached to the plate by a minimal amount of plastic on the front so the screw on the rear will allow it to move in or out for adjustment.  If someone does not understand or they are poking around under the front of the flywheel they can break this plastic adjustment tail off.  When this happens you will have throttle up to about 1/2 throttle, when the roller drops off the back of the broken part, the carburetor butterfly then drops back to an idle.  It is usually hard to twist the speed control grip back to slow because the carburetor cam has now dropped behind this sharp broken off part.


In the photo below the red arrow shows there this cam part is broken.  Normally the broken part will not be found so the owner does not know what is wrong or missing.   With the twist grip at about an idle position as shown, you will see the black plastic carburetor cam roller against the cam and under the RH edge of the arrow.


I am not sure whether super glue will adhere to that plastic or not.  Price of a new on is not that bad however.   It attaches by 2 short round protrusions that slide into mating round holes located in between the timing plate and the timing plate base.   When the plate and the base are screwed together the cam is held in place.


Broken cam plate on later motors, shown laying in position with a sheet of white paper inserted under it for clarity

  (10)   Timing Plate Loose on OMC 9.9/15hp :  This can be an item that may be overlooked, but it can be critical.  Under the flywheel is what I call the timing plate assembly, this is essentially the whole charge coil/ignition module under the flywheel.  It rotates when you twist the throttle twist grip.  If the "Ignition plate to support bearing" (#47 ) or part #322435, becomes worn or warped, it will then be loose, this will allow the whole timing plate to rotate under the flywheel by the force of the flywheel magnets rotating around the coils mounted on the plate.   This will cause the throttle timing to possibly change enough to create a non-starting motor.  This support bearing puts tension on the inside of the timing plate dia.  What usually happens is that someone oils everything up with this being one that gets a shot.  It needs FRICTION not lubrication.  You may be able to clean it up, then warm it in a micro wave, expand the ends to make it a larger dia.


This "bearing" is a fiber ring 5" in diameter, 3/16" thick and 1/4" wide.   It is has a groove around in the inside to fit over the plate, split in the middle like a set of piston ring to allow installation.   If it is collapsed, meaning it has both ends almost together, it will not be able to put enough pressure on the timing plate.  You may be able to put it in a micro-wave for a few seconds to soften it up, allowing you to spread it back out and be reusable.  When installed it acts as a bushing exerting circular friction between upper plate and the block.   The thickness up and down is not where the tension is put between the two but the outer circumference pressure.


There are 4 parts that constitute that this timing plate/stator assembly.  First there is reference #41 or "timing plate retainer and link", next #46 is the "support plate" onto which is attached #47 bearing, ignition plate support" which is a plastic type large ring with a groove in the center.  The outer edges of this plate #46 accepts #47 bearing.   This bearing is made larger in diameter and has angled ends to be compressed and ride inside the #39 "timing plate and sleeve" unit that the stator is attached to.  However it will not just slide on.


You will have to make a simple small wire staple that will hold the 2 ends in place while you slide #39 down over this #47 bearing.   The best I have found is to place the bearing so the joint is pointing straight to the rear.  Slide the timing plate assembly down, usually the staple will fall out, if not you can reach in with an ice pick, dislodge it from the bearing.  Now it will fall on top of the block, so you can retrieve it with a small magnet.  The red arrow in the photo below is pointing to the staple.  The other bearing shown below is the position the normal bearing is extended.  One is brown while the other is black, no real difference, but the brown one was a replacement, rectifying the black ones inability to stay expanded over time.


Shown below is #46 support plate with #47 bearing installed before assembly


  (11) Throttle Twist Grip Functioning:  It would be common however on the older cog gear throttle shaft linkage for wear to set in and there can be considerable slop in the twist grip settings.  If this is so, never go from slow to fast to set it for starting, but from fast to slow.  This can then position the timing a little faster and possibly set the carburetor at a slightly advanced position, giving a richer fuel mixture for the start situation.

Again for the early motors up to 1987, if the twist grip throttle handle (steering grip assembly) has developed enough slack that it is hard to find your position except if you move it from one way all the time.
  Or the engagement gears on the control gear and bushing assembly (#65) and the vertical shaft (#108) allow the gear teeth to jump out of mesh to where you may not be able to rotate the twist grip, you may need to make some shim spacers.  These shims can be made from the plastic of the sides of milk jugs, margarine tubs or other plastic bottles.


There is one screw (#62) on the underside of the twist handle that allows you to take the handle off.  Be careful when reassembling the handle as there is a internal thrust spacer between the spring and the handle that has 2 protruding lugs that have to align with notches on the main arm.  If you try to reassemble the twist handle and these mating thrust  spacer notches are not aligned, you can not get the handle on far enough to get the screw in.  You may need to twist things until the lugs engage, then after they are, you may again need to twist the handle so that the screw in the shaft align with the hole in the handle. this screw.  Be very careful that everything is square, properly positioned when you try to start the screw, as the shaft is aluminum and the screw is stainless.  If it starts but goes in cross-threaded, it will just get tighter, to the point that it will not go all the way in.  This can be a problem later, as the screw may not be able to be removed without breaking the plastic handle.  If it does cross-thread, it may be wise to get a 12-28 tap, clean up the threads in the shaft.


Twist grip & intermediate linkage for motors from 1974 to 1986 OMC 9.9/15hp


If you need to do any work on the gears, you will need to remove the large snap ring #67 in the illustration above.  To do this you need to use snap ring pliers, which can be a bear because of the limited area.  Once the snap ring is off the gear and shaft can be withdrawn from the front IF you tip the handle all the way up.  Look at the ends of the shaft as you withdraw it, as it has to go back the same way described below.


If the throttle twist gears disengage, (#65 & 66) you may be able to place a spacer on the twist grip shaft between the end gear and the housing, pushing the shaft rearward.  This can be performed without tearing any major parts of the motor apart.   I have used plastic off margarine tubs, made a washer that can be put on the geared shaft so it fits forward of #66 and against the housing.  This shaft and gear are spring loaded inside the twist grip so when shimming here it pushes #66 tighter into #65 gear.  If this does not help and the gears still jump the teeth then get out of time, then it is time for a new shaft with the new gears, price of $46.70 for both it and the matching nylon bushing.   You can weld new teeth back in or add bronze or silver solder to the tips to give more positive engagement.  The newer parts have both bronze teeth as compared to sintered steel, nylon or aluminum for the older units.


The pivot nut (#83) (shown in the pictures in the #7 section below) is really only a jam nut locking the bolt it is threaded onto from rotating in the arm itself when the handle is raised or lowered.  This bolt head is buried under the front bracket, which is threaded into the side of this bracket.   To get to it you need to go under and in the channel behind the front plate bar.  This bolt is again threaded into the base from the inside with not a lot of room to spare, so if you need to remove the handle you may need a 1/4" drive ratchet handle, appropriate socket (3/8"), with a extension and usually a universal joint.

If the handle is just loose, to tighten it, you need to loosen this (#83) nut, then tighten the bolt to the desired tension, then retighten the nut against the outside of the tiller arm.


Now there seems to be one MAJOR problem with these models, and that is that the twist grip is not really designed to be operated in any other position above a  35 degree angle.  If you tip it up farther and twist the throttle, you can experience these teeth to jump out of mesh 1 or 2 gear teeth without knowing what you just did.   When in this condition, it will usually run, but at about only up to 1/2 throttle.  It will not rev up to maximum speed as this flat will not allow complete shaft throttle movement. 


When this happens, you may luck out by again raising the handle all the way up, twisting the handle back to SLOW, then moving the handle down and hopefully re-engage the teeth.  There is a rubber cover on the top that does not allow you to see what has just happened.  These gears at the handle pivot have one large flat on each, about the spacing of 2 gear teeth which have to mate, acting as a timing situation and main thrust function.  When timed right these 2 wide gears should mate together in a position mostly in the upper position.


Farther inside is a vertical bevel gear (#109) that sits in the lower cowling is held in position by a separate plastic shaft (#107).  To get to this you will need to unbolt the vertical control linkage shaft (#108} that goes into this lower gear and attaches on it's upper peg to the timing plate arm.  


This bevel gear shaft  (#107) has a hollow center in it and can be removed by simply threading a 1/4" lag bolt into this hole, then raise the lag bolt, you can pull the shaft up and out of the lower gear and the base housing.  Mating into the gear #109 on the front is a horizontal gear (#52) that is connected to the front gear assembly (#65) by a intermediate shaft (#53) held in place by a snap ring  (#67) onto #65 gear.   These 2 bevel gears have a dot on one with a groove on the other, which need to be aligned.  In reassembling the intermediate shaft (#53) , to the gears, there are timing marks on all mating parts.  The shaft has square ends, mating with square holes in the gears.  The front end has 2 small raised lumps, the rear end has 3 small raised lumps.  These lumps mate into matching small notches in the square holes in the gears.

If your twist grip has a lot of slop in it, (meaning it rotates considerably before the timing plate moves) the snap ring #67 may have popped out of the groove in gear #65.  The photo below shows this snap ring in location.


Snap ring #65 in the shaft groove for a 9.9/15hp pre 87


If you get things out of time here, the mark on the twist handle will not align with the corresponding  "SLOW", "SHIFT", "START", or "FAST' or positions.


If you have slack between the handle itself and the linkage for the throttle plate, then you can shim (this shim will need a LARGE hole in the center) the bevel gear (#52) on the end of the intermediate shaft and the housing, pushing it rearward into a better mesh with the other bevel gear (#109).  As mentioned previously these shims can be made from old milk jugs or tops of discarded margarine tubs. 


The #109 and #52 gears are bevel gears mating into each other, it is easier to shim under the other bevel gear (#109) raising it for a better mesh with #52 gear.  #109 gear is pinned in a the lower cowling, rotates there against #52 gear.   Shimming UNDER the 109 gear is easier because this can be done without disassembling the front shafts and tiller handle.   You can make a plastic shim the size of the gear, again out of a plastic milk jug or margarine tub that has a center hole that the bevel gear shaft will go thru.  Slide this shim under the #109 gear, align the timing marks with #52 gear, put the #107 shaft in & reassemble.  This should force the #109 gear higher, meshing tighter with #52 gear because they are beveled and eliminate some of your slack.


These last two jobs will have to be performed after the manual starter, vertical control shaft and vertical control shaft gear are removed. 


Some of these abused motors will have enough slop in the gears/shaft/linkage that the twist grip will not align at the old START position in order to start the motor.  With the scarcity and expense of these old parts, it seems best to just remark the tiller handle base with a felt marking pen.


If you run into a situation where the twist grip is HARD to turn, there are a few things to look at.    (1) The #66 shaft may be corroded inside the plastic #65 bushing.  (2) The timing plate could be dragging somewhere.  To check this out disconnect the timing plate linkage at the #114 washer and cotter pin.  Now try the twist grip rotation again.  This should help you isolate the problem somewhat.  (3) The wiring cable bundle from under the timing plate may be dragging the top of the block or misrouted causing a binding.  (4) If you happened to replace one of the timing plate to base plate bearing screws, could it happen to be longer and binding on the top of the block?


(12)   Has the Throttle Twist Grip Teeth Jumped a Tooth or Two OMC 9.9/15hp pre 87? : Check the twist grip to see that it has not jumped a tooth at the pivot point where the handle lifts up.  If this is the case, your throttle indicator for START will not be in the right location relationship to the carburetor and the timing plate cam.  This could cause the motor to not want to start when the throttle indicator is in the START position.  And if it does start it will not be able to run more than 1/2 throttle as the twist grip linkage will be off the one tooth.  


AGAIN DO NOT RAISE the handle very high and twist the throttle at the same time for the 74-86 OMCs while you are running the motor unless you are prepared to disengage the gears, and change the twist grip timing relationship.  This is explained in a subsequent section.  Later, in about 1986 a throttle cable push/pull system was used to eliminate this problem.


You can check this by raising the handle, looking from the front at the mesh of the teeth on the 2 gears.    One has a WIDE tooth that has to mesh with the other gear that is missing a tooth.   If these teeth get out of mesh, about the easiest way to re-position them is to tip the handle as far rearward as possible, use a medium sized screwdriver, position the twist grip so it is aligned as best you can get it, then insert the screwdriver between the teeth, pry one tooth past the other and hope you do not break one off.  The other method is to pull the twist grip off, tip the lever rearward, slide the shaft forward, realign the teeth and reinstall the retainer screw in the twist grip.


The nut seen here is the #83 nut mentioned in the #6 section above.


Gears in mesh Gears out of mesh


Occasionally on the 86 and newer motors you may encounter one of the throttle cable systems that the twist grip will not stay where you put it.  The motor will usually slowly slow the speed down by itself if you let go of the twist grip throttle.  A solution shown in the earlier section for this was passed on by a retired marine mechanic.  His solution was to take a electricians #4 or #6 copper grounding split bolt clamp, simply clamp it around the throttle cable in an out of the way place.  There is enough room on these models to place it on the cable beside the carburetor.  Tighten the nut enough to just squeeze the cable inside the plastic sheath.  Works like a charm.


#6 copper grounding clamp squeezing the cable on a 1992 motor, placed under the tiller handle & taped for exposure. #4 copper grounding clamp squeezing the throttle cable on a 1994 motor


(13)   Is it Running on Both Cylinders? :  You might laugh at this question, but if it runs and has no power, or dies at an idle, is it running on both cylinders?   It will usually also be a harder to start when cold.   You would be amazed at how good a 2 cylinder outboard will run on one cylinder when just using muffs, but put it on a boat, just doesn't have any power.   I have even trolled all day long on just one cylinder firing.  Here was a situation that after traveling for an hour to get to the bay, I had no high speed power, simply would not rev up.  I knew there was a problem, but I did not want to take the time setting in the water at the launch to trouble shoot it, and trolling with my 70 hp jet would be about impossible.  I ran that 9.9 on one cylinder for 7 hours at a high troll speed, not a smooth idle mind you, but it ran and it saved the day.   When I got home I found the problem was a corroded  wire in the rubber coupler to the coil.


The tried and true method of checking whether it is running on one cylinder is while it is running at a low or medium speed, pull one spark plug wire off, replace it, then pull the other.  If it is running on just one cylinder it will die when you pull off the spark plug wire that is firing.


If it is only running on one cylinder, there could be many possibilities, and I would look at them in the simplest order first (1) bad or fouled spark plug.   (2) bad (loose or corroded) spark plug wire connections from the coil.   (3) bad electrical connections (again loose or corroded) in the rubber plug-ins or wire leading to the coil.   (4) bad ground wire connection, which needs to be clean and with no paint where it touches the block under the coil.  (5) the coil itself is bad.  (6) leaky cylinder head gasket allowing compression leakage.   (7) I have never seen a power pack on these 2 cylinder engines go dead for just one coil, (however it is possible, as have seen it happen on a 3 cylinder unit)

If you get to #6 and it is still dead, swap the coils from top to bottom, see if the non-firing follows the coil, if so then that coil is bad.  You will also have to swap the power in wires from under the flywheel, the depending on the year some are connected thru a rubber connector, which you can pull the pins and interchange them.

(14)  Neutral Safety :  (a) The OMC 9.9/15hp pre 87 motors and the 6/8hp 84 to 90 (along with others) are designed so that you CAN NOT start (by pulling the starter rope or engage the electric starter) the motor if the shift lever is in gear and the throttle is advanced beyond the start position.  This interlock is operated by the shifting lever.  The lever places the timing plate interlock so the throttle can not be placed in any speed faster than "START".   Another interlock where the where he manual starter spool interlock ratchet teeth has a dog lever on the top, or the side (depending on the year) of the spool that drops down, engages a ratchet that prevents the starter rope from being pulled if it is in gear.  You can pull the starter rope handle right off the end or break the rope, if you jerk the rope hard enough, are not suspecting that the thing is locked in the safety position.


(b) The timing plate interlock mentioned above blocks the movement of the timing plate until the shift lever is moved either into forward or reverse.  It is supposed to be set so that the motor will start in either forward, neutral or reverse but only run at a restricted speed.   If it is moved to forward, then maximum speed can be achieved.   On the early motors, 1974 for sure, this interlock does not exist. 

Some fishermen may disconnect or modify the above safety features if they use the motor for a back-up or emergency motor where every second may count. 


For the electric start models there is another but hidden push button type switch that is connected in line so that the shifting lever has to be in neutral for the starter button to activate the starter itself.


On this 1987, manual start motor, note the shift lever in neutral & the black plastic Neutral Safety lever stopping the rotational movement of the metal timing plate arm at the center of the picture just below the center of the flywheel.   On this 1983, with the shift lever placed in forward, the metal Neutral Safety lever timing plate stop has dropped down, allowing the timing plate to over-ride the stop by minimal clearance giving full throttle movement.   This timing plate is rotated by linkage to the twist grip throttle handle. 


(15)  Bad or Broken Reed Valves :  These are actually called Leaf Valves in the OMC parts books.  If they are not seating properly, this could contribute to hard starting, BUT it would be one of the last things I would look at if the motor has not been recently worked on.  If you suspect a problem with them, pull the air breather box off.  With the engine running, look for blow back through the carburetor, it should be real noticeable at idle if one is broken, as the carburetor should spit some fuel out the front and may even die.  Rather hard to detect however if it is bent or slightly misaligned.  Possibly low on power for one.


In the picture below, apparently someone took it apart, reinstalled the reed valves off set to one side on the bottom, leaving a gap as seen at the bottom arrow, creating a leakage for one set of valves.   The upper one has what appears to be salt corrosion under the reed and the plate.  These valves have to seat on the plate, (a good solid surface), no gaps, or corrosion.   The thicker U shaped parts that have the screws thru them are the reed valve stops, so that the thin valves do not get deformed by being pulled inward beyond their limits.   There appears to be some evidence of rust, possibly salt corrosion here.  Neglected or possibly a dunked motor.


One thing here, you will never be able to salvage the gaskets on either side of this valve plate as seen in the photo, so you will need new gaskets, one against the block and the other on the manifold side.


Occasionally the possibility exists that a reed valve will break, when this happens the motor will not run very well, you should be able to hear a sucking noise from the carburetor at low speed it it will run that slow.


Also when rebuilding a motor, you may find that one reed valve may not lay flat to the plate.  If this is the case look at the plate for straightness.  If the gaskets were stuck tight, you had to hammer or pry this plate off the block, you may have bent it.  If so simply lay it on a flat plate, using a hammer apply a slight amount of force in the proper location.  Once it is bolted back down, it will usually then conform.


In the Left Hand photo below the top arrow points to salt corrosion  under the valve and the bottom arrow is where a previous mechanic did not get the reeds positioned properly over the holes.


Another thing when you rebuild one of these motors, the reed plate/manifold gaskets do not interchange, at first appearance, they may look alike.  But they have different size holes for the reeds, so if you use the smaller hole size, (manifold side) gasket on the rear of the reed plate, the gasket reed holes will be smaller & will be holding the reeds closed.


This has not happened to me but was posted on one of the message boards.  The motor was hard to restart when warm.  It was finally traced to a small section of the plastic idle jet knob had broken off, sucked into the manifold, became stuck under one of the reed valves.  And the photo on the right below, also off the message board, is what can also get where it should not be.  This motor would run but was lacking full power.


Reed valve plate looking from the rear, or block side, corrosion under a upper reed & not a full seating coverage on the lower. Another reed obstruction.  Keep track of your tie tapes. 


(16)  Engines Revs, But Boat Does Not Move :  Most logically this could be attributed to a spun hub in the prop.  These props use no shear pin, being a thru the hub exhaust, use a rubber bushing that is bonded both to the splined inner hub and the outer prop body.  If for reason, (possibly hit something hard while running), this bond could be broken loose.  It could be tight enough to hold for say a trolling speed, but if you rev it higher, then the hub may slip inside the bushing, causing something just like a clutch on an older car slipping. 


This is easy to check, pull the prop off, look at the front of the prop and you can see the rubber hub between the inner metal splined hub and the prop body.   Here, scribe a reference line on the metal spline in line on the metal portion of the prop the hub sets in. Now put the prop back on the motor and go run it until the problem occurs again.   Pull the prop back off and check the reference mark. If the marks are no longer in line, the hub is spun.

These can be repaired by taking it to your marine dealer who will send it to a prop shop, as this is not really a do it yourself type of project.  However on a small prop like this it might not be cost effective.


(17)  Loud Clunking Noise at 1/2 Throttle Like it is Hitting Something ; (a)   Here, check the most obvious and easiest to fix first.   This would be a possible loose flywheel.   First try to tighten it.   If that does not help, then remove the nut and pull the flywheel, check to see if there is a ridge at the tip inside tapered hole.   If so file this ridge off, as it may be hitting the top edge of the crankshaft taper, and not allowing the flywheel to properly be sucked down.


 (b) This could be the shifting dogs jumping out under power. These shifting dog teeth are pretty hefty and deep so this is usually not a problem.   But if it is a motor that you do not personally know the history on, maybe in reassembly of the parts when doing a water pump repair, someone inadvertently screwed the shifting rod in or out of adjustment. 


Pull the lower unit drain plug, look to see what the oil looks like, does it have any metal filings or ground up metal in it?   Check the oil with a magnet.  The shifting shaft link may be bent or need adjustment to keep it in gear if that is the case.   Adjustment here needs to be done with how far you screw the shifting rod into the yoke of the lower unit when the lower unit is off the motor.   Hold onto the shifting lever and see if when it does this jumping, do you feel the lever wanting to move at the same time the noise occurs?  


I have also seen the forward edge of the clutch dog being worn slightly, this can cause the motor to jump out of gear on a heavy pull if the shifting rod is out of adjustment.  A cure for this can be simply when you reassemble the lower unit, to swap the clutch dog 180 degrees front to rear.   The dog slider gear is symmetrical and you have now just moved the worn forward dog to the reverse side where it will get a lot less use.


Or you could have a broken crankshaft.  These can break off completely, but since they are being held by three mainbearings, One on top, one in the middle and another on the bottom, they hold it rigidly enough that if the break is jagged, it will be held in place enough to run.


(18)  Crankshaft Seals :   Another possibility is that the engine may have worn/leaking crankshaft seals.  If this condition is bad, it will not allow sufficient vacuum on the intake stroke to pull fuel from and thru the carburetor.  This is usually the top seal that is bad.  This will usually be easy to detect in that it will make a mess under the flywheel, namely fuel/oil mix spilling down around the block.  It is possible to remove and replace this upper seal without a complete teardown. 


This area that can cause hard starting when cold is that the crankshaft seals can get worn and not allow suction from the back side of the pistons.  If either the top seal or bottom crankshaft seals are bad, this could lower the suction enough to not allow the engine to start.  The most likely of the 2 to go bad would be the top seal, because it will be more susceptible to moisture getting there under the flywheel, therefore rust on the crankshaft seal area.  The flywheel itself being heavy and rotating could wear the top crankshaft bearing slightly, allowing the top seal to deteriorate or become worn.   The actual determination that this is the problem may not be scientific, other than a somewhat sloppy flywheel side to side movement, but you could pour a slight amount of STP around on top of this seal around the crankshaft.   This oil is thick and sticky enough as to make a better temporary vacuum seal.  


Other than that, a defective seal will be just a guess until it is actually removed.   But the small price of the seal and minimal effort required to replace it could be a worthwhile guess after all the other tests and guesstimates have been expended.


This top seal is not that hard to replace as you do not have to remove the powerhead or split the case.  This top seal can be removed by a seal puller, or by driving a self-starting sheetmetal screw into the seal enough to get thru the metal, then screwing it in deeper by 1/4" to get a better hold.  Now you can get ahold of the screw with a pair of heavy duty slip-joint pliers, pry the seal up and out of the block.  You may damage it enough on removal that you may not be able to even tell if it was defective.  When it is out you can then check the crankshaft with a flashlight at the actual seal contact for rust.  If it is bright, clean the block area, using a socket large enough to slide over the crankshaft and to bear on the new seal, tap in down and into place until it bottoms out.


In the photo below of a 1974 9.9 hp, the finger is pointing to a white bearing ring.   Very early on they did make a white bearing, then black and finally brown.   And there should be no lubrication on these bearings otherwise the magnetic pull of the flywheel will rotate the timing plate, making for erratic running especially at lower speeds.


Evidence of a leaky top oil seal with lots of oil under timing plate with the early white bearing ring of a 9.9/15hp


I have heard of one of these motors that would start fine but would run only at full speed and then would need some choke to keep it running.   Initially it was thought to be the carburetor or the timing, but after much tear apart and adjustment, this one turned out to be the bottom crankshaft seal was bad.  This lower seal being bad is however an uncommon occurrence.


For the bottom seal replacement, you would have to pull the powerhead and possibly split the case just as you would do a complete overhaul.  Look at this as a last resort, but it will very seldom be the problem.


(19)  Power-head Seals & Gaskets :  If there happens to be a leak around any of the mating surfaces of the block you can also get problems as being a 2 stroke, the crankcase acts as a compression / vacuum chamber which can decrease the efficiency of the motor.  Check around the mating surfaces of the crank case for leaks.  With the engine running, spray some WD40 around the possible cracks, if the engine picks up rpm, there is a leak in the mating surfaces.


(20)  Bad Crankshaft Bearing Journals :  If the motor has been dunked, or abused so that water has entered the block in any way, and not taken care of immediately, you could have a rusted bearing journal on the crankshaft.  I have seen slightly tarnished journals that were in service with no indication of real failure yet.  One had the lower rod bearing cap was rusted to the point that there was pits in it.  It was obvious that this motor had seen internal water at some time, but had been run afterwards and was still running at the time of this tear down.  The reason for the tear down was worn rings, which may have also been caused by the water internally in the past as the cylinder walls were also stained, but not pitted.


This motor was put back into service with the same crankshaft but a polish job on the journals, new bearings and should continue to run satisfactorily for the average fisherman.


(21) If All Else Fails :  All the above is of course what you should be looking for as well as ASSURING your carburetor has been cleaned, floats set, timing synchronized, etc.  

While compression is important for compressing fuel before spark, the internal vacuum action of the piston also "works" (opens and closes) the reed plates.   Any air leak from bad gaskets, broken or poorly seated reeds, or bad upper or lower crank seals may decrease that vacuum in the crankcase and therefore it's a good bet why you have a bad idle condition.

One method of checking whether the reeds are closing is with the engine running at full throttle take a business card and hold it lightly by the long end about 1/2 - 3/4" in front of the carburetor.  The card should vibrate/oscillate.   If it saturates with fuel, your reeds are bad because the fuel is spitting backwards out the carburetor intake.

Use WD-40 or an UNLIT 16oz. propane torch and spray around the carburetor or manifold base, if the idle clears up, you have an air leak at the reed plate gaskets or carburetor gasket .   Do it again on any other junction of parts, looking for the same results.

There is also the possibility your ignition system or coils are going south, so check for voltage/ohm readings on those as well.  Again check ALL wiring connections.  Even replace the spark plug wires, rubber cover with marine, (not automotive graphite cored wire).  Make all soldered connections where possible.


If the spark plugs are always fouled, maybe you need to decarbonize the motor.  What you do in a case like this is to start the motor, let it warm up and saturate the internal parts with a carbon removing liquid like Sea Foam.  I have made up a 1 quart oil bottle with a 4' fuel line and standard fuel line coupler.  In this I mix a 50/50 solution of fuel and Sea Foam (about 1 cup is enough).  I then connect this to the fuel line coupler on the motor and run the motor at a medium speed until all the fuel is consumed.  Let it set for 1/2 hour to soak.  Start it up and run it.  You will get SMOKE and lots of it from carbon becoming loosened and then being burned.


This can loosen up the rings in their ring grooves of the pistons and remove built up carbon on the top of the pistons and head, giving the motor a chance at new life for a while.

Even doing a second shot at decarbing may not be a bad idea for neglected motors.


Here you can see my gravity fuel decarb kit in action


(22)  Twisted off Bolts During Impeller Replacement :  This may happen when you try to separate the upper housing from the lower unit.  If the 2 center bolts are the broken ones they are probably the least important ones and this hp of motor may well operate without them.  However here is a method if repair other than a complete upper housing replacement.


If the bolt does not readily start to unscrew, be careful as it may be seized and you are simply twisting the bolt.  With any more movement it may twist into.  If you suspect this, try to retighten a bit, the again try to unscrew it.  Usually not all are seized so by trying others you should get the feel of the ones that will unscrew as compared to the other seized ones.

The housing is aluminum and the bolts are stainless steel, not a good combination to remove in the 1/4" size.   So first off try NOT to break the bolts.  If a bolt does not want to unscrew without excessive force, try another to get a feel as to what it takes to break the bolt loose initially.  Then go back to the stuck one, try again.  If the bolt moves even slightly in a tightening direction, it probably is frozen, all you are doing is to twist the bolt.   Not a good thing.  In the photo below, the corrosion was between the lower unit hole and the bolt body itself, not in the threaded section.


Here you will see 2 holes drilled into both housings where penetrating oil was allowed to soak for a week.   Tapping the upper area with a hammer resulted in the paint being damaged, but it loosed the seized bolt


Here I use about a 3/32" drill bit and drill a hole in both of the housings where the bolt shank goes thru the lower unit AND into the upper housing where the bolt is threaded into.  Drill in just until you hit the bolt, go slightly into the threads.   You may want to be sure you even go into the bolt ever so slightly, but just enough to open a channel into the threads.  Put some penetrating oil into these holes. 


Tap the aluminum with a small hammer at this location.   The purpose of this is to try to get some of this penetrating oil to get into the shaft and threads.  The tapping may expand the aluminum slightly plus allow some of the oil to seep into the threads.   Let it set for a couple of days.   Tap some more, put more oil in the holes, try to unscrew the bolt.  If after about 3 tries of this, and you still don't succeed, use an Oxygen/Acetylene torch, heat the area at the threads to where the paint is burned off.  Put more penetrating oil in the holes, let it cool.  Try to unscrew the bolt again.  If it starts, then back it up to being tight, then loosen it again to just slightly more than the first try.  Keep tightening/loosening a little at a time until either the bolt unscrews, or breaks off.   These oil holes can then be cleaned and an epoxy or body putty can be used to fill the holes, being sure that the threads are protected.  Touch up paint is easier to do than breaking a bolt.


Now it would be best IF there is any bit of a stub of the bolt protruding to soak it with a penetrating oil  repeatedly for a few days.   Tap on this broken bolt as you soak it.  Then try to get a ViseGrip pliers onto what is protruding, slowly work it back and forth.   If it does not move even slightly soak, tap again.  If still no movement then heat the bolt with a torch as above, while warm soak again with a penetrating oil.  Note one of the best penetrating oils is common brake fluid or a 50-50 mixture of Automatic transmission fluid and Acetone.


Last resort would be to try and drill out the bolt, use an Easy-Out, but most likely you could not get the drill to center within the bolt as stainless does not drill very well, doing it by hand, the drill will run off.   Now when you have a hole partly in the bolt, partly in the aluminum housing, when you then try to unscrew it you may well  break an Easy-Out as you will be partly into the aluminum, binding the deal up.


Many times if a motor has been left with the lower unit in the water for extended periods of time, (like on a sailboat) where just the bolts into the extended housing will be seized.  This is not as bad even if numerous bolts become twisted off simply because once you have the extension off the motor it is easier to work on repairing the broken bolts.

A method I would use is to drill, roto-root with a Dremel Tool etc. to remove the broken bolt.  You will now have to tip the motor upside down.  Make a template of the bolt pattern, (thin aluminum or heavy paper) mix up a metal type epoxy, (JB Weld), pretty much fill the gouged out hole.   Spray a silicone onto the treads of new bolts, using the template to align the bolts, hold them in place and from tipping, insert the bolts doing a slight twisting motion to get the epoxy into the threads.   Let it harden to about 80%, try to slightly unscrew the bolts just enough to break any bond that may have occurred.  Let it set, when cured remove the bolts, file off any excess epoxy and reinstall.


One precaution here that may help someone at a later date would be to before you reassemble things to run a 1/4" X 20 TPI tap into each of these holes cleaning up the threads.  Then when you reassemble the unit, place a dab of anti-seize compound on the threads.


(23) Transmission "Stuck" in Neutral :   Do Not Force Shifting Lever IF Motor is Not Running.   One thing to be aware of on these motors, is that these transmissions (gearboxes) ARE NOT SYCROMESHED LIKE VEHICLES.  The clutch dogs in the gearcase's transmission are rather large in relationship to some other models.  This is good in that you most likely will not experience the motor jumping out of gear because of worn clutch dogs if the linkage adjustment is not properly set.  But also at the same time, it means that you should NOT TRY TO FORCE the shifting lever into a gear while the motor is NOT RUNNING because of these clutch dogs possibly not aligning when the motor is not running.   While it is running at a slow speed, these dogs are designed to engage easily.  Otherwise, you could very well break the shift lever, especially the newer plastic levers, or bend some of the linkage if the older metal lever.  If you experience this and you HAVE to place the transmission in gear with the motor not running where the shift lever does not want to engage, (as if the transmission is stuck) try slowly pulling on the starter rope just enough, and at the same time putting pressure on the shifting lever, to allow the clutch dogs to mesh into the gear recesses as they then become aligned.   Using this method, you find the spot you will be able to move the shift lever from forward / neutral and then into reverse easily.


Any time you may have a shifting problem, do not immediately question the gearbox, ESPECIALLY if you happen to be using a motor that is hooked up to remote controls.  The cables can become seized internally, or possibly stretched, out of adjustment or even become unhooked from the motor.  There are adjustments of the cables at the throttle/shift control ends.


As a test, if you do have remote controls, disconnect them from the motor and try shifting the motor manually at the motor as a test as explained above.


(24) Removed Wrong Screw When Draining Lower Unit Oil :  Here are two flat headed screwdriver slotted stainless plug screws on many of the MC motors, one in the front bottom of the right hand side of the lower unit (gear case) and the other above it by 6 to 7”.  The lowest is the fill plug with the top one is an indicator of when the unit is full. 


There is another round headed #2 Phillips headed screw above and forward the lowest flat headed slotted lower drain plug screw,  DO NOT TAKE THIS PHILLIPS SCREW OUT.   This Phillips screw is the pivot for the shifting mechanism in the lower gearcase.  If you take this screw out, then the whole lower unit MAY have to be disassembled to locate and reassemble the parts internally using a special assembly tool. 


However first I would try draining all the gearcase oil, lay the motor on it's side, (gravity is your enemy) use a stiff wire or ice pick, flashlight, prayer, beer AND are VERY LUCKY while having a steady handed friend slowly moving the shifter lever to realign it so you can locate the yoke pivot hole, get the screw back in place with the inner end going into the shift yoke pivot hole.   Be patient ... it may take quite a while slightly moving the shift lever, looking, moving, looking, ice pick probing, etc. to get the pin back in.  If this does not work, then remove the lower unit so it can be shaken a bit to maybe get that shift fork pivot hole in line with the gearcase hole.


This shifting yoke was initially installed as the first thing during the final assembly of the gearcase.  If you can not get it aligned by the above methods, then total removal of the shafts, gears and bearings may be the final alternative.  AND YOU WILL HAVE LEARNED SOMETHING, AND NEVER REMOVE THE WRONG SCREW AGAIN.


In the photo below this lower unit has been repainted so both of the screw heads are painted, otherwise they are normally the silver color of stainless steel.  This pivot screw is indicated by the red arrow.  The fill plug screw by a blue arrow.


Note this prop has the converging ring in place mentioned above.


(25) No Water Coming From the Overboard Water Indicator or Motor Getting Hot :  This is covered by an article all by itself.  CLICK HERE


(26) Water Coming out Between Housings if Using Flush Muffs :  When using the flushing muffs and a garden hose, you do not need to turn the water faucet valve on high, as it may be way more pressure than needed (like 50 to 60# as compared to the motor impeller normal output of maybe 15#) and can do possible internal damage to the powerhead IF there may be an unknown blockage.   


When running the motor under these conditions, if there is water coming out around the shifting rod hole in the lower unit, as shown by arrow below, the following can be the problem.  The rubber grommet on the outlet of the water pump, may not be inserted properly mating the pump housing to the copper tube that supplies the water from the pump up and into the bottom inlet into the powerhead.  This grommet is held into the water pump housing by 2 ears with the tubing going down inside it to form a seal.   If someone replaced the water pump or impeller and was not careful when reassembling the lower unit to the midsection during final slide up and bolt together, the grommet can get slightly dislodged.   You can not see this at the time of reassembly as it is not visible then.  It may be not bad enough to harm water flow during regular running in the water, (you could not see it anyway as this would be submerged then) but when running from the flush muffs, and more hose pressure is on than normal, water can be forced out at this area around the shifting rod.


Arrow showing possible water leakage location


This may or may not be a problem.  If the motor runs normal on the boat and shows no sign of overheating, there may a minimal concern.   However if there is ANY indication of minimal water, a decreased flow coming out the pee-hole, or any indication of it running hotter than normal, then I would tear it down, refit the old grommet.  Or, these grommets have underwent a design change making them more resistant to this problem happening.  They have better retention ears, are taller lending them to be more easier to become a slide fit covering more of the tube, for less of a chance to flop over.  One thing I recommend is that you apply a slight amount of grease on both the tube, in the grommet to facilitate this blind assembly process.


Another worse condition could be that the upper grommets at the powerhead, (both inlet and outlet) could be collapsed creating, #1 not letting cold water into the motor, or #2 lot letting the hot water OUT.   This would require pulling the powerhead for repairs as these grommets are located at the bottom of the powerhead.

(27) Engine Has Sat For a While :  If the engine hasn't been used in quite awhile, very possibly with old gas sitting in the carburetor, it may possibly require cleaning, which seems to be the standard recommendation for motors in this situation.  However, it may be worthwhile to try to run it at least once before jumping into a carburetor repair.  I have found that sometimes the gasket between the main carburetor body and the bottom fuel bowl can deteriorate.  When this happens, for what ever reason, chunks of the neoprene gasket get into the fuel bowl, can partially plug the high speed jet, cause erratic engine performance.  It has also been found that the newer non-leaded gasoline is less likely to cause internal gumming problems in the carburetor if allowed to set for extended periods of time.


Now with the new ethanol mix gasoline, this can create more problems.  Most motor manufacturers do not recommend over the 10% ethanol mix as outboard motor fuel.  This ethanol additive fuel will separate, if left in the tank or carburetor for an extended period of time without a preservative added will create more work for the mechanic.

The only way to fix a clogged/fouled carburetor is to remove, dismantle, clean, and rebuild it.  Do not try to spray a carburetor cleaner in the breather or run it thru the fuel, expecting it to do a cleaning job.  If you try this while the engine is running it very well could ruin the engine, as there would be little lubricant inside the engine for the bearings.  If you take the carburetor apart, make notes and drawings as to what goes where, or use a digital camera.  Regardless of how simple it seems, you will find something where you can't remember how it should be when it comes time to put the parts back together.


Also if it is an older magneto motor that uses points and condensers, it is very possible if you can not get any spark, that the points have oxidized.  Running a strip of crocus cloth through the contacts sometimes does wonders.


(28) Engine is Seized & You Have No Idea Why :  Here you will have to do some detective work.  Look over the outside of the block to ascertain if there is a broken connecting rod that may be protruding out a hole in the block.  Put it in neutral and see if it still will not pull over.  Try to rotate the prop, what you are trying to determine is that the problem is either in the powerhead or the gearcase.  Can you rotate the flywheel any amount?  There will be some slack in the bearings and connecting rods, but if it the pistons are froze up, it will not rotate more than a slight amount.  If you get the flywheel to rotate a quarter turn or so, then it could be a broken rod. 


Or it could be that the gearcase is seized up.  This could be due to lack of gear oil, but usually it would be because a seal was leaking and water leaked in, then not used for some time, creating rust.  If this motor was used in salt water, then usually the price of the bearings, gears make the repair not worthwhile.  You might be able to pick up a complete gearcase unit on eBay from a blown powerhead motor for less than 1/2 the price of new repair parts.


Either way, you will probably need to (1) pull the lower unit as if you were going to replace the water pump.  If you get the lower unit off, and the motor will crank over, then you can be assured that the problem is in the lower unit, not the powerhead.   (2) if pulling the manual starter will not allow the motor to turn over, pull the head, which may help give clues as to if it is in the powerhead area. 


(29) Engine Has Been Hot & Seized :  This will more than likely be caused by a non-functioning water pump, or something wrong with the cooling system.  It could even be from a fouled carburetor or someone forgot to do a oil/fuel mix and the motor locked up.  In this situation, the pistons more than likely have expanded due to excess heat, since the aluminum pistons expand more than the steel cylinders, the pistons can get seized in the cylinder bores.   If the motor was running fast when this happened, the flywheel will be still rotating which will put a lot of torque on the rods and will usually break or badly bend a rod also.   Many times the rod will break, the part still connected to the crankshaft is flying like a airplane prop and will blow a hole in side of the block.


If the block is OK and the rods survived, but the piston just seized in the bore, by pulling the head you should be able to decipher what has happened.  If the cylinders are scored, it may be best to tear the powerhead down, check the pistons and rings plus the actual condition of the cylinders.  You may be able to just hone the cylinders to repair that damage.  But at this point, since the unit is torn down, the cost of new rings would be low in my book.   Buy a set and do the job right.


(30)  Engine Has Been Dunked :  Obviously this situation will need  IMMEDIATE ATTENTION.  You will have to pull the spark plugs immediately after recovery, pull the starter rope over enough blow any water that is inside the motor out.  Spray WD-40 in the plug holes, crank it over numerous times, spray more WD-40 in.  If it is fresh water, you will be able to clean the motor and salvage it.  I would first pull the carburetor, clean all the water out of it.  I would also recommend that you immerse the carburetor in denatured alcohol.   This is so that the alcohol will absorb any water that you can not blow out with compressed air.  The alcohol will then evaporate, taking the water with it.  Without doing this you may have to run it for MANY hours at a not to successful situation trying to get the water out.

You will also have to look at the electrical system.  There are rubber connectors on the wiring that should be disconnected, cleaned any water out of the connector holes.  Use alcohol as a cleaner as it will absorb the water, then dry with no residue.  If it is a motor prior to 1977, you had probably pull the flywheel and clean the points.


I would then place it in a large 55 gallon tank, as compared to muffs, as you will need to run it for many hours to dry thing out.  Then you can try to restart it.  A few squirts of starting fluid into the air breather tube may make it jump into life, but don't overdue it as starting fluid has no lubrication qualities as compared to a mixed fuel.  Mix a fuel oil mixture twice the normal ratio, like 25-1 as you need to lubricate the internal parts of this motor, that is the way a 2 stoke engine is lubricated on the pistons and internal bearings, is with the oil mixture with the gas.  Once you get it running try to keep it running at a speed above idle, because you need to dry out the water and lubricate the bearings and crankshaft.  This is also a good time to after a few hours of running to readjust the carburetor for an idle. 


I recovered one motor that had been dunked (not running) in freshwater for 2 weeks and it is now running fine.  For a link to this article CLICK HERE


  (30-a) Engine Has Been Dunked in Saltwater :  In a situation like this you will need to totally disassemble the motor, clean all the salt off VERY SOON.   If you can not get it torn down soon, submerge it in fresh water to help dilute the salt (actually a good idea anyway).  And I mean TOTALLY disassemble it as if you were rebuilding it and do it ASAP, like within hoursThe lower unit should have survived since it is sealed to keep the gear oil in.


  (30-b) Engine Was Running When it Was Dunked :  This will be a totally different situation, but will also require total disassembly, as that the motor will have sucked water into the carburetor, which may have built a something solid (water) inside the crankcase when the piston comes back on the fired stroke.  Usually something will break inside the motor, most likely it being a connecting rod.  At very least the rod may become bent.


(31) What To Do if the Lower Unit is Dry of Oil :  This can be a scary situation, especially if you just purchased the motor used from a friend/neighbor.  Is it just out of oil, or is there any evidence of water in the gearcase?  If it is just dry because of a leak?  But usually if oil leaks out, then water can leak in.  And if the motor was used in salt water, then the bearings could be damaged.  Is the lower drain plug loose, or even VERY TIGHT?  If it is real tight, then possibly the previous owner knew there was a leak somewhere, he was trying to plug it by TIGHTENING this plug.  


If the gearcase was dry, I would refill it with Kerosene, crank the motor over in both forward and reverse gear if you can.  If the motor runs, you might let it run with the Kerosene in the gearcase in gear for a few minutes, shifting gears a few times.  Let it set for a few days, then crank it over again, then drain it out, catching the oil in a plastic margarine tub.  Let this drained Kerosene set for a day, then carefully pour it off, leaving whatever residue there may be in the bottom of the tub.  This residue will give you clues as to the internal condition of the gearcase.  If it is just black sediment, you might be OK, but if it has metal filings or gritty gunk that is attracted to a magnet, then possibly the bearings are worn.  This test will determine your next course of action as to whether you simply refill it with gear oil, replace the plug, filler screw plastic seal/washers and hope for the best, or you may have to actually tear it apart to see what is wrong.


On the 1979 motor mentioned above and shown with all the oily, rusty pistons, it also had a BAD lower unit.   No oil at all in the gearbox.   After the Kerosene flush all I got was rusty brown gunk when drained.   I could not even pull the prop shaft out of the housing with a puller (bent the puller).  And the drive shaft was rusted so solidly into the pinion gear, that by even placing the shaft in my large lathe, moving the carriage back to where it could apply pressure and someone else beating on the other side with a block with a 4# hammer, nothing would move.   It is evident that there was probably saltwater inside it for some time.  This whole lower unit is just scarp.


Another place to look for leakage is the prop shaft seals.  If the motor happened to have monofilament fishing line wrapped around the shaft in front of the prop, it can be on so tight that it could have been forced into the seal, ruining it.  


(32) Motor Starts But Will Die if Shifted Into Gear :   Has this motor been used as a fishing trolling motor?  If so you may have sizable amount of monofilament fishing wrapped around the propshaft in front of the prop.  Since it was wound on in forward, it can become tight, but in neutral there is no power to the shaft and in reverse the rotation of the shaft is different, which could possibly allow it to not bind up then.

I have seen monofilament fishing line wound so tight around the prop shaft that you could start the motor in neutral, but when you tried to put it in gear, the motor could not overcome the friction at this low shifting speed, it would die.


 The picture below shows that this mono got so hot that part of it molded itself into the seal recess, actually looking like it could have been the seal at one time.


Monofilament fish line taken from around the propshaft in front of the prop


(33) Motor Starts and Runs Fine but Vibrates Bad When Quickly Decelerated :   If you are running it in a garbage can and take the prop off so it will not throw water out when you shift it in gear, this has happened to a young friend of mine.  He brought it to me to find the problem.   In my barrel this motor would start fine, run both at an idle and high speed fine, but when you slowed it down quickly it would kind of miss and vibrate badly for a short period of time. 


He had replaced the water pump impeller a couple of years before and this year the complete ignition system, points, condensers and coils (a 1975 15hp Evinrude).   I noticed it was not pushing water in my test barrel.  I asked if he had brought his prop, he installed the prop and the problem went a way.  It appears the motor was designed to work under power using the prop and when he left it off when you quickly dropped RPM there was not any resistance on the driveshaft and it vibrated enough to effect the motor.


(34) Electric Starter :  We are assuming here that when you push the starter button that nothing happens, the starter motor does not engage and there is no noise from the starter at all.  (A) Here, the number one check would be, are the battery cables properly connected to the battery?   There will usually be some method of identifying the HOT from the GROUND wire, be it color, a ribbed grove, etc.  If there is a RED color wire it goes on the Positive side of the battery.   (B)  Is the battery up to a full charge of 13 volts?   (C) Check to see if the shifting lever is in neutral , as this activates the neutral safety switch and breaks contact to the starter.  (D) Is the negative battery cable properly grounded to the motor's base?  (E) Is the starter button itself functioning?  (F)  Is the starter free to spin?  (G) Is the starter drive gear free to slide UP the shaft to engage the flywheel ring gear?  (H) Is the main starter wire to the starter intact with a clean contact at the mounting nut?  (I)  Has someone had the starter off, possibly broken the electrical internal wire off at the starter under the nut?  (J) If the motor is 1987 or newer, is the clip under the red kill button?  This is needed, as without it you are the same as having an ignition key turned off.


If you are working on a post 93 version, there will be an additional part added in the system, a starter solenoid.  This model uses a considerable less heavy duty push button switch, requiring the use of the solenoid.  This is covered under the post 93 article.


(35) Motor Mounting Clampscrew :   The 2 clampscrews that hold the motor to the transom may need service occasionally.  The pivoting handles of these screws should have oil placed on the pivot pins from time to time to keep them from seizing up, then breaking off.   To service these screws, it is best to remove them from the bracket.  There is a smaller screw that comes in from the rear and is screwed into the rear of the main clampscrew, holding on the large cupped washer.  Use a 7/16" socket wrench to remove this smaller screw, then you can unscrew the clampscrew, totally remove it from the bracket, clean then replace.


Somewhere in production before 1983 the clampscrew handles were changed from aluminum to a high impact nylon and the screws themselves made of stainless steel.  This made handles more susceptible to breakage but the stainless screws was an improvement.  You may want to keep these screws well oiled as replacement screw assemblies cost $31.84 each, as of mid 2005 and you may need one for each side.  If you prefer not to purchase new ones, you could use a standard course 5/8" bolt with the old washer bearing against it.  This would be a hassle if you were taking the motor off and on boats repeatedly but it would work.

These screws can become seized if neglected, especially if the motor us used in saltwater, to the point where it takes a pipe wrench to loosen them.  Of course this will ruin the threads.  You may well twist off this 5/8" aluminum bolt in the process.  If this happens, you need to locate the center of the broken off bolt that is still in the clamp bracket & use a center punch to indent the center.   Then drill it out with a 3/16" drill bit as close to being straight with what is left of the broken off bolt.  Next move up to a 1/2" drill, remove what is left.   If you did not get it quite centered, no big deal, even if you nicked the threads a little on one side.  Now you can make a cape chisel, which is basically a regular punch of about 1/4" diameter, grind the tip end on a slight angle.  With this now sharp tapered edge, you can usually get in on one side and tap the chisel with it pointing slightly in,  pulling some of what is left into the 1/2" hole you just drilled.  If you can not get it loose, get a oxygen/acetylene torch, heat the inside of the hole trying to break the corrosion bond.   Then use the cape chisel again.  When you get it out, then run a  5/8" x 11 tap thru the threads to clean them up.


In this area also, later at about 1990 there were zerk grease fittings installed in the front of the tilt hinge shaft boss.


(36) Friction Adjustment Screw :   On the LH side of the midsection tower is a large headed screw that has a heavy coil spring around the screw and under the head.   This is for adjusting the motor's vertical pivoting shaft so the motor does not rotate so easily that it will not stay in a straight forward position without you holding onto the tiller handle especially when trolling where you need to change lures.  This is one screw that can very well become seized because the early motors up until about 1986 had a screwdriver slotted screw with it and the tension spring buried into a recess in the midsection housing.  If it became partially seized you could not get enough pressure by the screwdriver to loosen it.   If the motor was used in saltwater, this is one place that since it is "out of sight" it will not be removed, oiled with any frequency.  Then when the pivot bushings get worn in, become loose, you need to adjust this screw, it is about impossible to move.  You do not want to break it off as without a total tear-down you can not even hope to drill it out or re-tap the hole, since it is a blind hole terminating at the pivot bushing.


Below on the left photo is a seized early screw that the "protective spring's sleeve" has been chipped away allowing salt debris to be somewhat cleaned up.  In preparation to try to remove this screw, the housing was drilled with a 1/8" hole into the boss, just touching slightly into the screw threads.   Then a slit was cut down into the screw threads with a # 409 Dremel tool part off stone.   It was heated up with a Oxy-Acetylene torch and a ball pein hammer tapped on the housing in preparation to try to remove it.   Penetrating oil was applied on the spring base, in the drilled hole then allowed to set for a few days in hopes of breaking the corrosion loose.   SUCCESS SMILED HERE. 


You will notice the difference in the newer unit in that the screw is longer, the spring rests against a outer boss on the base, as compared to the early shorter screw with the spring being buried inside of what was a protective sleeve type hole in the housing with only the screw's head protruding, which makes for salt corrosion to hide in.   Here part of the sleeve was broken away to allow access to the corrosion in this hole and around the spring.


This early type seized screw with internal spring being removed with the motor tilted up The newer hex head screw & a external spring with the motor in the run position


Now in repairing, this unit was be cleaned and a new 1/4" X 20 machine bolt with long enough threads to reach from the outer part in, coated with a boat trailer axle grease.   The drilled hole and slot was filled with JB Weld.  When this is almost cured, the bond (if any) will be broken allowing the bolt will be backed out enough to be sure the bond is broken.  


You can not match the newer configuration because the older type screw hole was farther forward than the later ones, if you try to use the new longer screw it will hit the transom bracket when the motor is tilted into the run position.   Then purchase a new late type screw #321531 and spring #551113.   Cut about 1/4" off the threads of the screw to give needed this clearance.


Repainting finishes the job.   The new screws have both a screwdriver slot and a hex head, the hex head will be what is used as you can not get enough tightness with even a large screwdriver.  This time before installing them, coat the now spring base hole with a liberal amount of the waterproof trailer wheel bearing grease.   Install the spring around the screw and in the hole, more grease in and on the spring.  Screw the screw in until you get the desired tension, pack more grease around the spring completely filling the pocket.   Wipe off the excess.  And remove it every year to be sure it is free and can be adjusted when needed.



(37) Driveshaft Seized in Powerhead & Lower Unit Will Not Drop:  About the only way to separate the driveshaft from the powerhead in this situation (especially fro the 9.9/15hp, but usually most others also) is to REALLY get aggressive on the wedges between the exhaust housing and the lower unit .   Number one, you need to get it dropped enough to remove the shifting rod securement screw.  If it is seized beyond that, you can try to tip the motor upside down and soak a quart or so of penetrating oil for a week or better, trying to get the oil into the upper driveshaft spline and the lower part of the crankshaft splines. 


What will happen with more wedging is that you will need to force the lower unit down and the water pump impeller key up THRU the top of the water pump’s plastic housing.  Once it breaks this pump housing, the driveshaft should slide up thru the pump housing, as it is just splined into the drive gear in the gearbox.  You might even do some damage to the exhaust housing by the wedging, but Bondo or JB Weld is your friend here.  However the best wedges that do not damage things are loggers timber fallers plastic power saw wedges.

Then you will need to pull the powerhead so you can get at the upper spine and be able to remove the driveshaft.  Then more soaking with penetrating oil, but at least you can be closer to your work and get more persuasive.


(38) Excess Play in Prop : If you encounter a situation on a 9.9/15hp where the prop has considerable forward/aft movement consider this.  There needs to be a thrust washer (brass for early motors or nylon for later) between the rear of the prop and under the prop nut.  This thrust washer is about 1 1/8" OD and is splined to match the propshaft on the inside.  I have checked the 3 motors I currently have from 74 to 92, one had prop movement of just under 1/8" down to barely noticeable on the others.  If you have considerably more forward/aft movement in the prop when it is installed, someone has left out the thrust washer.


Oh $hit : Shown in the photos below is an example of what can happen if you use a lesser, or no oil in the fuel mix for a 2 cycle motor.  These crankshafts however was not off a 9.9, but an earlier series motors that has only bronze rod bearings which required a richer oil mix of 24-1,  not roller bearings like the 9.9s allowing a 50-1 mix.  However here I suspect NO OIL was mixed with the fuel, as what you would normally see if a lower ratio was used for an extended time would be the wrist pin in the piston would seize up first.


But the photos show such a good example that I could not pass it up posting it here.  I acquired this blown motor in a box of spare parts, so know nothing about the actual cause.


In the LH photo, it pretty well ruined the crankshaft and everything else closely associated with it.  From the looks of the connecting rod, it must have been making considerable noise just before the world ended for the boater.  It appears to have stopped so suddenly that the flywheel key was sheared.  I know nothing about this one except it was in a box of parts motors that I got from a outboard mechanics widow.  The photo on the right does not really show all the roughness in the rod journal, BUT IT IS BAD, BAD.


An example of what can & does happen if the laws of mechanics are not played by This crankshaft was also ruined  but apparently by a weak oil mix


Here is a thing that a boater does not really want to see


Replacement Parts : There are a couple of good online marine dealers that seems to have factory parts for most models is .    The other is  Their websites have a online illustrated parts listing.  Their parts appear to be discounted off retail prices.  They even have a parts technician that you can call to verify if you encounter any questions.   I am not sure how old of models that they carry parts for without doing a lot of looking, but I had no problem getting water pump parts for a 1977 Mercury 4.5 hp or parts for a obsolete Sears 1986 15hp Gamefisher. 


On the Water Test : One word of advise is when doing a on the water test, is to never run downriver or farther from the launch than you can easily row or paddle back.


Copyright © 2004 - 2019  LeeRoy Wisner  All Rights Reserved

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Originated 11-2004, Last updated 04-11-2019
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 Tri-flow spray lubricant, Just spray it in the cylinder or carb etc. it is a great lubricant but in addition it is very flammable, maybe even more so than starting fluid or carb cleaner. I used to use pre-mix in the cylinders on problem motors or just trying to bring a oldie to life, Now I only use this product it is a bit pricy but I have found nothing that works as well.



flywheel key for pre 93 9.9 motors which is .156" (5/32") wide X .715" overall length.