1974 Johnson 9.9 won’t slow idle

[Flipper89]

I bought the motor as a project thinking it just needed a new water pump. I replaced that and it will start but only runs above the “shift” position on the throttle. Below shift, it will sputter/sneeze and die. Also, possibly related - I noticed a small leak of water from the top of the head gasket, I just slowly bubble out near the top right bolt (looking at the engine from the back).

I have not cleaned the carb yet - I want to get an idea if that may solve the problem or if it’s the gasket leak. Thanks in advance!

 

[Tourtney]

Sounds like it could be a fuel problem. I would say to soak the carb for a day or two as a starting point. Be sure to get the jets clean especially. Be sure to check temps of the engine make sure it’s not overheating.

 

[Crosbyman]

those shift / start markings can be deceiving ...if the motor runs good don't worry about it but water bubbling is different


torque the head bolts to spec or….. open up the cyl head plate to inspect the gasket if the problem is not solved with proper torquing.

 

[oldboat1]

^^agree. Add that you should resurface the mating surface of the head cover -- wet/dry sandpaper on a hard surface until the shine is equal all around. The reassemble as described.

Assuming the leak is handled, try to dial in the air/fuel mix. Start with the needle out for seated about 1 1/2 turns. Let it warm up, then try to slowly set the mix a bit leaner (clockwise) until it stalls or lean sneezes. Back the needle out about 1/4 turn and see if it will smooth out. You also have a carb idle setting (knob on the side of the pan, I think), and should try to get it to idle in gear at about 650-700 rpm (slow idle). If in the driveway, you should make these adjustments with the leg in a trash can or similar, with water maintained at about half way up the leg. (need back pressure) Idle or fast idle only.

 

[flyingscott]

Those motors never idled well. The first 3 yrs of that model were not great. Run NGK plugs in it keep the points clean and hope for the best. Did you see water out of the head or the waterjacket cover. Even OMC could not get that version to run good.