coleman kayak1
Petty Officer 1st Class
- Joined
- Aug 8, 2005
- Messages
- 260
Motor: 1998 Yamaha C40 Not Oil Injected; Mounted on an 18 foot pontoon boat
Since we repowered with this motor it has given us nothing but reliable year after reliable year. Unfortunately this year we ran into some problems.
At any speed above idle, the motor runs normally. We see the same WOT speed, runs just fine, etc. etc. Idle is where the problems start. Idling in neutral, it runs normally for a few seconds then "coughs" and almost dies, then recovers and runs, the repeats itself. In gear it does the same but usually dies. As you can imagine its a pain in the butt trying to dock or load on the trailer, much less troll (which we do a lot of).
So we did the usual stuff first, changed the plugs, ran seafoam through the gas, and replaced the fuel filter. No change at all. I was told by a reputable shop it was a lean condition, but the carburetors are all fixed jet. I used the propane torch to check for vacuum leaks, and didn't find any. We also decarbed it, which we do every year anyway, but it didn't help anything either.
When its coughing you can pull the bottom plug wire off, and it makes no difference. Of course rev it up and it falls on its face, but I can safely assume its the bottom cylinder giving us the problems. I held a card in front of the carburetor and it seemed to get more "stuff" on it then either of the other two, pointing to a sticky or bad reed valve? Weak diagnosis I know but its all I got to go on.
Just looking for some input. We're in the middle of redecking so we probably won't worry with the motor til next spring, but if I had something to go on we may tackle it this fall. Thanks in advance.
Since we repowered with this motor it has given us nothing but reliable year after reliable year. Unfortunately this year we ran into some problems.
At any speed above idle, the motor runs normally. We see the same WOT speed, runs just fine, etc. etc. Idle is where the problems start. Idling in neutral, it runs normally for a few seconds then "coughs" and almost dies, then recovers and runs, the repeats itself. In gear it does the same but usually dies. As you can imagine its a pain in the butt trying to dock or load on the trailer, much less troll (which we do a lot of).
So we did the usual stuff first, changed the plugs, ran seafoam through the gas, and replaced the fuel filter. No change at all. I was told by a reputable shop it was a lean condition, but the carburetors are all fixed jet. I used the propane torch to check for vacuum leaks, and didn't find any. We also decarbed it, which we do every year anyway, but it didn't help anything either.
When its coughing you can pull the bottom plug wire off, and it makes no difference. Of course rev it up and it falls on its face, but I can safely assume its the bottom cylinder giving us the problems. I held a card in front of the carburetor and it seemed to get more "stuff" on it then either of the other two, pointing to a sticky or bad reed valve? Weak diagnosis I know but its all I got to go on.
Just looking for some input. We're in the middle of redecking so we probably won't worry with the motor til next spring, but if I had something to go on we may tackle it this fall. Thanks in advance.