Johnson_carb

ohnson, Evinrude, OMC, outboard motor, outboard motor repair, 9.9, 15 hp, year of manufacture, powerhead, piston, water pump, carburetor, long shaft, 15 hp conversion, sailmaster

Items Covered Here: This section will cover all the 2 cycle 9.9 & 15 hp carburetors, carburetor timing & fuel pumps, but keep in mind that there may be a few slight differences depending on the year of manufacture.

Carburetor : Do not think that you can up the horsepower by simply modifying a existing 9.9 carburetor by replacing the main jet with a 15hp main jet. All you accomplish is that the engine is being fed too much fuel & not enough air to properly mix with it & the engine will then blubber (floods out) at the top end. It can run OK on the lower end & idle OK because it is using the idle jet then, but it will have less top end power than with the original 9.9 main-jet. Believe me, as I have been there/done that. Matter of fact that is what years ago got me into writing the original of this article so I could document & remember myself, as I could not readily find any factual information on the subject, only speculation from so called experts. To reiterate the above, a modified 9.9 carburetor using a 15 hp main jet WILL NOT work.

Factory specification rating for RPM of the 9.9hp is at 5000 & the 15hp at 5500. With operating range for the 9.9hp at 4500 to 5500 RPM, & the 15hp at 5500 to 6500 RPM.

Carburetor, early : Early production motors had all metal carburetors. Then from about 1980 to late 1987 the same basic carburetor as previously was used, but had a black plastic bottom fuel bowl. This plastic seemed to be an improvement in that if water had entered in the system & got in the bowel, then sat for a while creating RUST inside the carburetor & even enough rust on the outside if used near saltwater to corrode holes in it. If you have to replace the metal bowel the cost is $24.00 as of 2005. I have however seen metal fuel bowls on 1982 to 1987 carburetors, however I am not sure if the carburetor was ever changed or just the bowl. Or there may have been a supply of metal bowls on hand on the dealer's shelves if the plastics had gotten cracked.

The older floats are made of varnished cork & can get deteriorated over time & may not function properly, if so replace it with the newer black plastic type.

If the float bowl gasket on the carburetor is black, it is the older composition cork material used for bowl gaskets, & the float will usually be cork also, then you are probably way overdue for a overhaul. There could be pieces of this cork gasket floating around inside the bowl, occasionally plugging the main jet. The float should be OK unless the varnish has deteriorated.

In the LH bottom photo, you will note that the cam roller pivot arm is white plastic & with an adjustment screw. This would have been a later unit in that series because the early arms were made of steel with no adjustment. Some of these carburetors are missing the throttle cam roller & arm unit.

	Carburetor, 1974 to 1979 metal fuel bowl	Carburetor, 1980 to early 1987 plastic fuel bowl	Late 1987 to 1992 with plastic top & fuel bowl
RH VIEW
LH VIEW		Need a good photo here yet

Carburetor, late : Late 1987 & newer production carburetors up thru 1992 were completely different & had the bottom fuel bowl & top made of heavy black plastic. The choke lever is the same in these newer carburetors even though the motors used the cable twist grip which utilized a totally different throttle system.

They were apparently designed for easier manufacture as the plastic top has the idle jet in it & the juncture between this top & the main body serves as a passage (depending on the the gasket) for the fuel from one chamber to the other. There is a white nylon collection box that is sandwiched & gasketed between the main body & the bottom fuel bowl that has a removable main-jet on one side. These carburetors appear the same for the 9.9 & the 15 hp with the exception of the main-jet AND the throat dia. in the main body. In the parts list, the main-jet for the 9.9 is spec'ed out at a hole #34 (.055dia), while the 15 is #54 (.110 dia.). The idle jet suction tube comes off this collection box & goes up into the plastic top for suction to the idle jet itself. This arrangement appears to help keep debris out of the jets.

The choke butterfly is the same as the previous models, but the throttle plate is smaller. The internal throat of the 9.9 is about .500 dia. while the outlet hole into the manifold is .750 dia. This is quite a bit smaller than the earlier versions, & the guess is that this newer carburetor is probably more efficient. It appears to have all the screw holes & outboard fittings in the same locations, but whether it would interchange with the earlier versions & function reliably is something I have not tried, but I suspect it would function OK. However some of the the internal castings of the intake manifold appear different also. OMC repair kit #439073, or NAPA /SIERRA part# 18-7219.

If it is more efficient, then the motor will possibly idle better & have less of a black oily residue ooze out of the lower part of the exhaust housing for weeks after it is put into storage. One other observation while the carburetor is off, you will notice the intake manifold has a slight vertical separator on the bottom section up about 3/16". The supposition is that this may help fuel flow to the individual cylinders better. These later carburetors also had an adjustment screw for the cam follower.

Both these older & newer style carburetors up to 1992 use the same air box or silencer, but to most of us it is known as the air breather.

If you see a carburetor advertised on e-Bay that does not have the above RH side choke lever, but only a shaft protruding with a roll pin installed, it will be for a 1993 or later motor, as the choke lever is different.

There then was another twist that you may encounter & that is a remote controlled motor that has a electric choke. On these there is a small solenoid with a wire running up to the choke lever on the carburetor for activation when you hit the remote choke button.

Update Carburetor : This info came off a e-Bay sale item. "The original carburetors used on the 1988 -1992 9.9 HP had a plastic cover which didn't have a sufficient number or retaining screws that let the cover flex on acceleration and could cause stalling or stumbling and poor idle. The new carburetor, part # 436779 is a factory update carburetor which replaced these defective plastic bodied carburetors. Dealer cost was $244.42" It is not known whether this was a factory recall on this, but probably just if you brought it in & complained. Now that OMC has sold it surely is not honored anymore.

Removal of the Carburetor : You need to remove the plastic carburetor intake cover (OMC calls it a silencer). However the early ones I have seen are white instead of the common black color that is on the later versions. It just could have been that some motors that had white ones that were made of a material that did not survive vibrations as I have seen may missing. Remove the choke lever & the idle knob. When removing the idle knob, make note as to the location where the indicator tit is pointing, as you should replace it in the same location when reassembling.

You also need to remove the recoil starter unit. The manual starter unit can be unbolted with the one 9/16” headed bolt head in the center of the recoil unit. Be very careful as that spring is dangerous! Pull the rope out a few feet and tie a slip knot in it so that it can't rewind back. Carefully remove the starter handle, then grab the rope inside at the starter pulley, then let the rope withdraw somewhat but not completely (leave a foot or so to work with). Now, secure the rope inside at the starter pulley to the upright pulley gear guide in a manner that will prevent the spring from rewinding the cord etc. Hold the manual starter assembly together when loosening the top large retaining bolt (do not remove that bolt completely from the starter housing assembly). Carefully remove the starter assembly while holding it together. Screw a 3/8" nut on the bottom of that large retaining bolt to hold the starter together while you're working on other components.

There is a small coil spring (#1 in the photo below) from the carburetor to the ratchet of the starter & up to about 1979 that needs to be unhooked. This spring's tension is released by a lug that the timing plate cam positions when the twist grip & shifting lever are in neutral. If the throttle is faster & the motor is in gear this black plastic dog drops down into the starter spool teeth, not allowing the manual starter to be pulled. This dog's function will still operate by gravity if the spring #320490 is missing, but not as positively. This spring is obsolete & only available from aftermarket suppliers at a cost of $9.95.

There is also a Z link rod (#2 below) This ties the roller bar unit to the throttle valve of the carburetor. Do not loose it either, or a makeshift one will need to be fashioned as this #2 is below from a piece of welding rod. The important thing here is to get the bends just right so that the timing is consistent when the timing plate moves this roller forward to give movement in the throttle valve increasing fuel flow.

Clean & Rebuild the Carburetor : Remove the fuel line. Disassemble the unit. Once the carburetor is off, unscrew the bottom screws that hold the sheet-metal bottom pan on. When removing this pan, be careful & try to save the gasket if you are not going to get a repair kit. Remove the cross pin that holds the float, remove the float & the needle valve. You will need to also remove the idle shaft screw, count the revolutions it takes before it comes out. In this way you can replace it with the same number of revolutions when you reassemble it. If the insides are dirty, you can get a can of carburetor cleaner & spray on or soak until things soften up. Usually you can use an air hose to blow thru the passages & be sure they are clear.

The illustration below is a copy of OMC carburetor repair kit instructions dealing with the 1974-early 1987 carburetors.

In the illustration above, you will notice the #6 needle valve & seat that the needle has a small wire clip shown. This was not on the early, (possibly 3 or 4 years of production). Where this clip goes is, it slides into a groove in the needle & then the other end goes over the flat part of the float pivot plate just ahead of the pivot pin. In functioning, it ensures that the needle is retracted when the float drops as the fuel is used. It could be possible that if the needle were to stick up (closed), & did not open to allow fuel back into the carburetor, the motor would starve for fuel.

There is one solution that works great to soak carburetors in, it is any of the outboard de-carbonizing liquids. One that is universally available at even automotive supply stores is Sea Foam http://www.seafoamsales.com/ that is used as a fuel additive to help unstick hydraulic lifters or run it in the gas to decarbonize piston rings. It will not damage any of the rubber parts. Just soak it overnight.

You can possibly get by without a repair kit or gaskets if you are careful in your disassembly do not use a gasket sealer when you reassemble it as some may dry out when the motor is stored over the winter & some of this sealer may dry out & chunks of it can get in the main-jet. Later gaskets were a neoprene type positively does not need any sealer. If it just had debris & water in the bottom, you can get by without a repair kit. But if it is gummed up varnish you will need to go farther. Check the idle needle valve for straightness of the tip, if it got dropped, this tip can get bent. If you are good, you can possibly straighten a bent one, otherwise just get a repair kit.

For the price of a $12.75 repair kit for the early versions, while about $21.75 for the later style. You get all new gaskets, needle valve, main jet & new metal plugs that are needed to replace the old ones if you have to get all the channels cleaned out, and float adjustment instructions.

When reassembling, place the float back in position & replace the cross pin. Be sure that the small wire clip is attached to the needle & the tail is over the float plate. Tip the unit upside down & check the float height. The now upside down unit should have the top of the float parallel with the now top of the housing. If not, you can adjust it by bending the metal tab that acts as a stop for the float. Be sure that the float & needle can move up & down freely, otherwise if either binds, the motor may run at different speeds depending on how much your boat is tipped to one side or the other or raised in the shallow water drive mode.

Screw the bottom pan back together & reinstall the carburetor onto the motor's intake manifold. Remember to reattach the small spring on the starter ratchet if it was made prior to about 1982. On the later plastic topped carburetors, you will find numbers near the attaching screw locations. These are for the tightening sequence.

When reassembling the idle jet screw, & you forgot how many turns it was set at, a good starting spot would be to screw it in until it lightly bottoms out, then back it out about one turn. After you get it running & slowly lower the speed, try to turn this screw either in for out for a better blend of air to fuel mixture at an idle.

Reinstall & Adjust the Carburetor : After reinstalling the carburetor to the intake housing & you need to reinstalled the choke knob. The choke knob shaft has a slot in the middle that the carburetor's choke lever goes into. This shaft needs to be installed with the longest length of the slot upwards, otherwise the choke lever does not have enough room to function. Now you need to re-install the plastic carburetor intake cover. The idle knob is next. Even after you replace in the same location as it was before tearing it down, & you get it running again, you may need to fine-tune adjust this idle knob for trolling.

There is also a large knob on the left hand side of the lower cowling on all but the very early years motors. This large knob activates an internal threaded rod that acts as a stop for the throttle plate linkage & is used for a slow speed setting, (not to be confused with the actual carburetor idle settings). After 1987 this knob was discontinued when the cable throttle system was instituted. The new slow speed setting was then changed to a twist knob on the end of the twist throttle.

After the motor has been run enough to have it warmed up, try to let it idle. If it runs to fast or slow you can adjust the large knob stop screw on the motors left hand side. It may be best to initially do this with the motor cover off, so that you get an idea of which way to turn this screw. Turning this knob counter-clockwise pulls the threaded rod out & makes the motor run slower.

When you get the motor running at your trolling speed, then turn the carburetor idle screw knob (lean/rich) clockwise a slight amount, let the motor run for a few minutes, & rotate it slightly more in the same direction again. Doing this you are making the motor run leaner. Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting & the smoothest the motor will run at slow speed.

When you have finished the above adjustment, pull the knob off forward & reinstall it so the pointer in the "DOWN" position. You will now have a "GO TO" position if need be, which will be discussed later.

It make sense when shutting down the motor for what may well be a extended period of time, to disconnect the fuel line & run the motor unit it dies, using up all the fuel in the carburetor.

One part that seems to find legs a & wonder off is the is the linkage rod from the carburetor throttle plate to the cam follower. In the illustration below is the dimensions for it if you need to fashion one. These appear to all be the same from 1974 up until about 1986 & after that there is a different number that has a slight "V" bend front to back.

Timing : The throttle cam plate that rotates under the flywheel when you twist the twist grip & the plate has an raised line 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 (RED ARROW) in the photo below. To adjust this on the older motors, you loosen the 2 bolts on the RH side of the plate & adjust the cam plate to where it just aligns with the roller at the same exact time that the throttle plate begins to rotate. For the newer motors, the plate is shown below is made of plastic & has a adjustment screw on the outside (PURPLE ARROW). They also have another adjustment screw on the throttle cam roller unit.

To tell when the throttle shaft starts to rotate, take a small alligator clamp & attach a short wire to it, as if you were attaching a electrical wire under the screw head. Clamp this alligator clamp indicator unit onto the end of the throttle shaft (BLUE ARROW). Now you have some indicator way better than just watching for rotation of the shaft. The flywheel & air box were removed here for clarity.

In the photo below, you can see the timing mark by it being the lighter colored raised part at the right of the arrow's point. The older aluminum timing plates also have this same style of mark. This timing plate needs to be adjusted as the roller is away from the timing cam plate by probably .030".

One thing that needs to be pointed out is that if you change carburetors & or complete ignition systems is that possibly the two may not really be compatible. Meaning the carburetor roller can be a different diameter. If you happen to get one that the roller is smaller than the original, you will get a situation like the photo below where the roller does not touch the cam plate mark when it should. This would give you an engine that may starve for fuel & hesitate before you advance the twist throttle more. And it may never achieve full power.

The timing mark on the timing plate cam does not need to touch the roller at the low end (or idle) of the twist grip rotation. On these motors, at low speed, the the timing plate will move counterclockwise AFTER the carburetor cam movement& throttle butterfly valve will stop. This allows the timing to go where the motor runs at it's slowest before it would die, while not moving the butterfly valve, & if the low speed side of the carburetor, (the carburetor air jet idle screw) is set right.

Alligator clamp	Timing the carburetor throttle shaft to the ignition timing plate

If you are having problems locating a start position on your twist grip throttle setting because of obliterated wording, or if you have a remote throttle, a method of locating the timing "START" position would be to advance the timing plate to where the carburetor arm roller just touches the timing plate cam, then advance it about 3/8" (9-10mm) more. This positions the timing & throttle at about the start position in the carburetor.

Fuel Pump Repair/Replace : Typically this size of fuel pumps were used on about all the 2 cylinder engines in the same year range, from the 2.5hp up to the 55hp models. The fuel pump is normally pretty trouble free device. These pumps are activated by vacuum created below the pistons of the motor thru a hole into the inside the motor’s side plate that leads into the crankcase. If a problem occurs, check the 2 hold down machine screws & the neoprene gasket under the fuel pump. There is also a filter screen on the outside of the fuel pump.

The older pumps are basically the same as the new ones with the exception that the new bodies have 2 external tabs, that align with the diaphragm tabs & other gaskets to help make it easier to assemble the parts correctly. The repair kits do not even list a kit before 1982. You however can use the new kits in the older pumps if you are careful & replace the new parts just as the older parts came out. Price on a rebuild kit is about $12.00. There are 2 spring activated check valves, one on the suction & the other on the outlet. There is also a small spring & plunger inside all this, making it slightly hard to keep everything in the proper locations while making the final assembly. It is suggested that you use the 2 longer attaching screws as guides in from the back side to align things before the final assembly. Do not be surprised that you may have to do back & reassemble it a time or two before you get it right. One word of caution, do your repairs on a clean LARGE uncluttered table as the parts are small & may tend to crawl off & hide. Also read & understand the instructions that come with the kit. CLICK HERE for link to 1959-1987 factory rebuild info. Or HERE for 1987 -1998

Early fuel pump from about 1959 to 1987	Later fuel pump from about 1993 on
Photo coming

The new fuel pumps are different, from about mid 1987 on, but the old type was still used for the rope starter versions while the new type was used on the electric starter models. The new type was moved to the LH side of the power head. A 5/16" NF threaded hole was tapped into the original fuel pump vacuum location with a hose fitting allowing the hose to be rerouted behind the head to where the new pump is located just in front of the electric starter. This new fuel pump was not designed specifically for this motor, as it was also being used on almost all of the larger motors of this date.