Front view showing timing cam & roller	Control panel for a post 59 Johnson motor showing both high & low speed jet adjustments with the choke knob on the left

 

    These carburetors have a built in glass fuel filter / settling bowl at the bottom.  The air breather, (they call it the air box) is attached to the front of the carburetor.  The choke knob is screwed onto the brass linkage rod from the front.  The nuts holding the carburetor onto the manifold are 5/16" and use a 1/2" wrench.  You have to pull the choke out to access the RH nut with the wrench.

 

    When you take it apart, it is advisable to count the outward revolutions of both of these needle jet shafts so you have an idea as to were to return them to.  These floats are made of varnished cork.  Unless the motor has been stored with old gas in the carburetor, the float should still be usable.  The float level is set so the float is parallel with the body when turned upside down.  This is done by bending the brass tab at the rear of the needle for the shut off.

    In cleaning up the 1957 motor, the carb was darned clean, BUT the cork Low Speed Nozzle Gasket had hardened enough to not survive being reused.   The newer repair kits have a Neoprene gasket #0344037 at a price of $6.41 if sold separately.    However a plumbing Neoprene flat washer #3/8M (which is about .112" thick) can be modified by drilling a larger hole in the center .243" then treading it onto the needle shaft, and rotating it on a course sanding belt to achieve a diameter of from between 7/16" and 1/2" OD.

    One suggestion, when removing these carbs, take a photo of the spring tension system around the low and high speed needles.   These put tension on the Johnson front panel.   However do not take it as being totally correct, (like some DIY mechanic) may not have replaced them correctly.  But anything is better than trying to decipher what goes where off a exploded part diagram.

    ANOTHER thought, if the motor is having starting problems, these motors won't start if the high speed needle is adjusted wrong.  When turned to the start position for cold start it's the high speed part of the carburetor that comes into play here, not the low.   Also make sure your needle stem packing is new for both, and that the main jet is backed out enough for it to fire as described below.

 

    In the photos below you can see the bottom or high speed jet along with it's linkage to the control knob. The knob operating this jet slides over a octagon sleeve around the idle jet shaft.  The low speed needle which is the top one, screw it in to a lightly seated position and back out 1 1/2 turns.  The high speed needle which is the bottom one is 3/4 turn out from lightly seated position.   Run it in gear under load (at a fast run), adjust high speed in until it starts to die then back out until it runs smooth. Slow down to idle and adjust low speed in until it slows down or starts to cough and back off until it smoothens out.  You can loosen the high speed linkage rod and adjust the linkage so that the dial is set where you want it.  I also like to slip the low sped knob onto the shaft so the pointer is pointing straight up.  That's all there is to it.   

 

     If you are having starting problems, and you are sure the ignition is OK, fuel or the choke may not be operating properly for cold start.  Spray come mixed fuel into the carburetor and see if she fires off.

Anyway, it shouldn't take more than 10 minutes to pull the intake manifold and check the reeds to see if a bug or whatever is blocking them open. 

   In the photos below you see the close-up of the carburetor and the newer type breather/silencer.    

 

    As this series advanced, the factory made changes, (with this series probably having underwent the most cosmetic surgery of all the other models).  The previous models utilized the carburetor dual knob system with center knob as the idle adjustment and the lower knob as the high speed adjustment.  As seen in the RH photo below, this is reversed with the high speed in the center.  This is because the main motor cowling was changed, putting these adjustment knobs in the lower part of the cowling instead of higher in a separate front panel.  Now the high speed adjustment is directly in line with lower needle (high speed), instead of using a linkage rod to activate it.

 

 

    Reed Valves :   Stuck open reeds will keep the motor from being able to push fuel into the crankcase, thereby preventing it from starting.  However, stuck open or closed reeds will have no effect on compression because the compression reading is off the top side of the piston.   The reeds open and close, sucking fuel into the crankcase from the carburetor because of the osculating suction/pressure off the bottom side of the pistons.

 

 

   Many times if they have sat for a number of years, crud/rust may accumulate under the seats of the reed valves.  But they're rarely the problem, however if you are pulling the carburetor to clean it, you really should pull the manifold and check the reeds JUST IN CASE.

 

    If it's bad reeds, the motor should still crank up and start momentarily if fuel mix is sprayed directly into the spark plug holes.  If you decide to pull the manifold to check the reeds, be very careful if you choose to pull the intake that you remove every screw!  There are a couple of hard ones to spot inside the manifold that must be removed before it will come off.  If you pry on the manifold with much force you are guaranteed to ruin it.  However I wouldn't pull it unless it will start with fuel in the cylinders, but not without it.

 

    Motor Mounts :   The rubber motor mounts are pretty well designed, a rubber block with attachment bolts molded into them last a long time and are externally mounted.  The actual runner mount is the same for both the upper and lower, but the lower has a housing around it that also clamps onto the pivot shaft as shown in the photos below.

 

 

    Upper Cowling Mounts :  These rubber mounts are susceptible to breaking, especially the rear ones as the rear of the cowling is what is normally used to help lift the motor up and puts a lot of strain on these rear mounts.  These tend to have the bonding from the bolts to the rubber deteriorate and may separate from the mounting bolts.    It is also rather hard to remove the usually rusted nuts from the bolt studs to even try to re-bond the rubber.  The originals are made of a thick round rubber that has a stud screw bonded to both the top and bottom.  If you have the powerhead off, you could make replacement ones from 1/4" all-thread and some thick rubber, about 5/8" (I am guessing here as to get to them it takes pulling the power-head).  Otherwise it is probably the best would be to try to clean them and then use Super Glue. 

 

    They are usually just left alone unless you are doing  are rebuild with the powerhead off.   Leaving them broken, the result is not detrimental to the running of the motor, except the upper cowling when snapped to the lower part has some movement and can make a rattling noise when running.

 

 

   Clamp Bracket Screws :   These screws that hold the motor to the boat transom threads are  1/2" X 13 TPI or National Course.  If you can not find any replacement ones then a simple 1/2 NC bolt  3" long or with at least 2" of threads and with a flat washer under the threaded end will suffice for a considerable time.  It may just not be a pretty looking as the original, but it will hold the motor to the boat.  Most of these screws are damaged by neglect of not maintaining them with a small amount of chassis grease or Vaseline before they rust or corrode in the bracket.

 

    Shown in the photo below is a built in location to use a chain from the motor to the boat for safety sake.

 

 

   Shaft Length Change :   If you need to change from a short shaft (15") to long shaft (20"), lots of luck in finding the 5" extension required to make this change.  Drive-shafts, shifting rods and water tubes can be lengthened the 5", BUT IT IS A HASSLE. 

 

    Changing a long shaft to a short shaft would be easier.  As you might find a used driveshaft like I did for less that $50 including shipping, and then I can sell the complete long shaft kit to someone who really needs it.   Or, just remove the extension, shorten the driveshaft (cut and weld in the middle) and shorten the shifting rod upper part from the gearbox and the water tube from the water pump.  FYI  short shaft length is 25 1/2".

 

   Welding the driveshaft (either shortening or lengthening) would be best to take it to a machine shop/welder, as afterwards the shaft will need to be straightened in a lathe by slight bending "adjustments" numerous times to get it to run as true as possible.  If the welder is hesitant, then have them also make, and slide a stainless steel sleeve over the weld and weld it in place also.    Just be sure this weld is up above the water pump and in the exhaust cavity area so it does not interfere with the water pump.   The only thing that might interfere is IF it is the version is where the lower drive gear is not splined onto the driveshaft (but pinned), replacing the water pump impeller will require total disassembly of the gearbox as it would need to be assembled differently (if even possible).

 

    Drive-shafts were different on the early motors (QD10s at least).  These shafts are 1/2" diameter, and the older ones had 11 splines top and bottom.  The later ones used 4 spines to and a woodruff key at the bottom drive gear.

 

       Remove Lower Unit :   In getting the lower unit (gearbox) off, here is the procedure.
  

    To access the shifting lever coupler when removing the lower unit, there is a small cover on the right hand side of the exhaust housing retained by a screw top and bottom.  Remove this cover then you can then get to the coupler and remove the bottom screw to disengage the upper shifting rod from the lower rod in the lower unit.  Now the lower unit should drop down and be loose from the rest of the motor.

 

     In replacing this screw upon reassembly be careful to get the groove that the screw goes into centered in the screw hole before you attempt to insert and tighten down the screw.  The one I worked on had a tendency to slide up too far which could bind the screw when it was tightened, stripping the threads.  A flashlight and slow movement of the shift lever is needed in this situation.

 

 

 

   Gearbox :   If it runs pretty much OK in neutral, but bogs down in any gear, then possibly you have a lower unit / gearbox problem.   Unscrew the large headed slotted screw (not the Phillips screw) in the bottom area of the lower unit.  What comes out?  There should be a dark thick 90 W gear oil.   If it is a thick creamy color it has water inside.  If no oil comes out, your unit probably has a leaky shaft seal, which may have let water in and then over time also drained out if not ran for some time.  If this is the case then you may have a rusty prop shaft or gears.  Either of these will put a lot of excess resistance on the motor when shifted into either forward or reverse, causing it to bog down.

 

    The lower unit gearbox is NOT the unitized type as used on the later 9.9s but has a bottom section that when the unit is turned upside down, exposes all the gears and output shaft.  There is a spaghetti type O-Ring that seals the grease in the lower unit when assembled.

    There appear to be 3 different midsections/gearboxes fitted to these motors over the years.   From it's inception in 1949 to probably 1955 was the first as seen below.   Here the shifting rod is accessed directly under the powerhead and accessible by removing a upper rear cover.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    

Here is a stripped down QD-12, with totally different midsection	Here QD-12 powerhead is shown

 

   The gear box was changed in 1958 from the larger 5 bolt lower unit to a smaller 4 bolt unit.    Also there was a internal change in how the pinion gear (drive gear in the gearbox) was attached to the driveshaft with it being changed from a friction fit onto the driveshaft to a splined fit.   It appears that all the other gears, shaft and bearings remained the same.  This change came about 1959/60, as 1960 parts list shows 2 different part numbers for the pinion gear.

 

    For the1958 and later, if the rear seal (prop shaft seal) is leaking you will need to replace it, factory #303345, the NAPPA / Sierra part number 18-2022 has the same shaft .554" dia. but smaller OD (1.00") and wider .375".   While you are there you might as well replace the rear bronze bearing housing O-Ring also (1.062 ID X .125 thick).  NAPPA / Sierra # 18-7117.  The whole NAPA gear housing seal kit is #18-2682.  For those of you with the 1957 version  or earlier, I am not sure if these parts fit or not, HOWEVER I suspect most of them will.

    To install the new prop shaft seal, be sure the hole in the bearing housing is clean, lay the housing endways (front down), align the new seal, start it by hand if possible.  Then lay a flat piece of steel on the seal, tap it in with a hammer.  This way it can only go in as far as the housing allows as the flat steel will stop because it is hitting the housing.

 

    When you reassemble the shaft and shifting slider dog, be sure that the slider yoke is positioned as shown above.  Also the bearing housing has a hole that engages a peg in the upper housing that secures it and keeps it from rotating, be sure that is in the right place before you tighten down the cover.

 

   This gear case does not use a regular gasket, but a spaghetti rubber seal is .100" dia. allowing the two metals to mate tightly.  This seal is purchased in bulk so you cut off just a bit more than you need.  For this model 11" is enough. This seal is the same as used on all the other models that have the split gearbox, it may just be a different length depending on the size of the motor.  It may do the job alone, but OMC recommended it's 3M 847  sealant, but it's kind of pricey hard to find at regular stores.  Lots of folks use Permatex #2 Ultra Black with good success and it's available at almost any auto store for just a few bucks.  The main thing is that you want to keep it watertight.   Also when you lay out the rubber seal in the groove, cut off just a little longer than needed as it will spread out in groove when housing is pressed together.

 

    When reassembling these gear cases, you should use some gasket sealant on the spaghetti seal itself, both surfaces of the clamshell gear case as well, especially around the bolt holes as well as the perimeter of any oil seals.

 

    If you can not find outboard gear oil, go to a automotive store and purchase 80-90W non synthetic gear oil.  This would be as close to what the factory originally used.  I use the same oil in my rototiller gearbox.

 

    The old 10 hp prior to 1958 had the larger 5 bolt lower unit which were the same as the 15's and 18's had in that same era.   The front 4 bolts use the same pattern as the later 4 bolt gearboxes, where it is possible to interchange a 5 bolt pattern onto a 4 bolt pattern, just the rear bolt/stud would extend rearward and not be used.

 

 

 

    If your motor slips out of gear, you either are missing the shifter lock detent bar on the side of the powerhead, your clutch dog and gears are worn out, or the shift linkage is worn out. Or all three.

 

    Water Pump Repair :   This water pump impeller replace job is a simple after you have removed the lower unit. 

 

    Water pumps are basically the same design as still used on all outboard motors.  These impellers are a larger diameter than on some of the later unitized lower units, in my book they appear to be able to still function even after many years of usage even after becoming less flexible.  The one thing the early units,  was that they were made of a pot-metal cast housing that after years of neglect, (especially if used in salt water and not thourohly flushed) the normal deteriorated condition it will be well worn or corroded inside (as shown below).  It is then recommended to replace the pump unit with the newer nylon housing with a stainless steel liner version (that is still available) if you have plans on using it in salt water and keeping this motor in your stable for some time.

 

 

Here is the early pre 1955 water pump without the cover	Here the mid version this one being  a 1957  --  5 bolt version	And the later 1959 version  -- 4 bolt version

 

    What I have found is the early (1949-1955?) have a 1/2' shaft with 11 splines top and bottom.   The impeller would be Sierra 18-3002 which was  2 3/4" in diameter, 1/2" thick, with a 9/16" shaft hole and has 6 vanes.  The overall length of the driveshaft was 25 3/8".   The 3 screws holding the top metal cover are located so that this plate will only fit in one location.

 

    The next version still used a 1/2' shaft, but used a totally different water pump housing, while still using the Sierra 18-3002 impeller.  This shaft again has the 11 splines on top and bottom with a overall length of         

 

   A change was made in 1958 with a different lower unit which also included the water pump and impeller, which coincided with when the upper cowling was also changed.  These used what was known as the 4 bolt lower unit.  The pre1958 impeller is the same as the 10, 15 and 18 hp of the same years and used that water pump and the Sierra 18-3002 impeller and has a 1/2" diameter shaft.  The 1958 and newer, are the same as the 9.5 hp series which followed this model.  The impeller used on these later motors is 2 3/4" in diameter, 1/2" thick, with a 9/16" shaft hole and has 6 vanes.  Sierra  #18-3003 is the number.

 

    In the LH photo below, note the nylon O-Ring at the top of this pump housing.  This slides into the motor's mid-section and ensures shaft alignment..   The black color water pump housing is just a painted pot metal unit as seen at the upper O-Ring section.  I have not been able to readily find the newer type nylon housing for this model as used on most of the later motors so I am not sure that they even exist now.  

    The 1957 that I worked on apparently never saw salt water, as no corroded bolts anywhere AND the water pump housing was in excellent shape, compared to other pitted ones I have seen.

 

    Any person familiar with normal outboard repairs should be able to replace one of these impellers in 20 minutes.  The most time involved will be re-alignment of the driveshaft and shifting rod.   The Clymer flat rate manual says it should take 1.3 hours.   However I have found that if you remove the starter unit, then stand the motor upside down on a stool, it is a lot easier for one person to do all three alignments Driveshaft, Water Tub, and Shifting Rod.

 

 

     It is recommended you replace the water pump to outlet tube grommet as well.   This grommet is held in place by 2 "ears" on the sides that snap into matching holes in the top of the water pump outlet tube.

 

     Many times the grommet has been known to not slide over the tube properly, therefore giving a chance to allow the outlet water from the water pump to leak somewhat.  So it is beneficial to lightly grease the lower end of the tube to help it slide in better.

 

Shown below is the water pump grommet, note the "ears"

 

    The lower unit gearbox is not the unitized type as used on the later 9.9s but has a bottom section that when the unit is turned upside down, exposes all the gears and output shaft.  There is a spaghetti type O-Ring that seals the grease in the lower unit when assembled.

 

    OR you can use the garden hose muffs and try to cover the reverse water intake scoops, then with a folded grease rag cover the water intake behind the prop.  Then wrap a small garbage bag liner around the rear of the housing including the grease rag and tighten a ratchet strap around holding the grease rag tight.  Kind of a redneck approach, but in a pinch does work.

 

   Prop :  In the early/mid 1970s OMC offered a accessory Lexan prop for the 9.5 hp.   That is all they offered for a short time was the replacement 3-blade, 8 1/8 diameter, 8" pitch prop (part # 385940) but later they dropped them and reverted back to the aluminum props.  That same prop was also spec'd as the replacement prop for 1958 - 63 10 hp motors.

 

    The prop is secured by the old style, using a cotter pin thru a threaded plastic nose cone, using a 9/16" X 16 thread.  It is a 3 blade aluminum secured to the prop shaft by a 3/16" dia. by 1 5/16" long shear pin.   The prop has a 9/16" hub hole.

 

 

    The 1960 Johnson motor that I worked on had a distance between the transom clamp area (where the top of the boat transom would be) to the cavitation plate of 18".   The owner thought it was a "Long Shaft", but upon measuring from the clamping area which would be the transom to the center of the prop it was 22", the same as most all later short-shaft motors.    The difference was really that the prop was a smaller diameter with the cavitation plate closer to the prop.  I also suspect that this was common before the later motors labeled "Short Shaft" became standard at 15" to the cavitation plate.

 

    Black or Gray Oil Coming Out of the Lower Unit Holes :  Many of these motors (especially these older motors that have to use a richer fuel/oil mix) are basically used as a secondary motor, and usually then as a trolling motor, which are ran for considerable length of time at a lower RPM.  The fuel oil mixture ratio of 24-1 or even 32-1 is probably too rich for this type of usage. The black oil that seeps out of the motor is  just unburned oil from the gas mixture.  The black color is coming from the carbon created during the pistons firing situation and is accumulated unburned inside the exhaust housing.  When the motor sets for a while the excess unburned oil in the fuel is mixing with and softening up the carbon, creating the black oozing oil.  You can reduce the amount somewhat by properly adjusting the carburetor idle jet to it's leanest position, also where the motor runs best at an idle. 

   This black or gray oozing oil could be also because of a stuck open thermostat which would not allow the motor to warm up.  However thermostats that get stuck usually do it in the closed position, so a bad thermostat is usually not the cause of this condition.

   Or, it could be a 6 gallon tank that the fuel line is still attached to the motor during storage while the outside ambient temperature is high enough to expand the fuel inside the tank to where the gas is forced into the  carburetor and IF the needle valve is leaking, it will force fuel into the engine and out the exhaust which mixes with the exhaust carbon, then leaches out as BLACK oil out the prop's exhaust.

 
   If you are getting a thick creamy gray oil oozing out the drain hole on lower unit, it is essentially the same as above except the inside of the housing may have less carbon build up, therefore the color will be lighter.  It is the same thing as described above, but possibly from a new or rebuilt motor that may not have been run much for some time and there is not a lot of carbon inside the exhaust housing.   If there is minimal carbon built up from previous runnings, the oil will be the thick creamy light gray color that has a lot of water mixed in it.   This could also be caused by the converging ring (#332395) is missing on the prop.  This plastic ring facilitates a suction from the outside of the prop when the motor is running at a slow speed to help suck more of the exhaust gasses away from the "thru the prop exhaust" when idling in neutral or running slow.

   This oil seepage may not be evident until a day or even a week after usage, then will seep out up to a couple of months later.  Most repair shops just recommend that for most boaters to then simply live with the idea that you may have to wipe it down after each usage. 

 

    You could also see this oil seeping out of the front lower unit water drain hole.   It is observed that if these motors are used on a smaller boat as the only propulsion, and act as a "get there" motor and also as a trolling motor, this black residue is considerably less to almost non-existent because the motor gets hotter because of the faster RPM, where the motor has a chance to warm up, thereby "burning" some of this excess oil.