maj_hazard
Cadet
- Joined
- May 20, 2008
- Messages
- 15
Seems I lost my first attempt at posting this so I'll try again..
I have an odd problem with my 1986 Johnson 40 HP. The engine has a random miss that only appears at low RPMs and mostly during idle. The idle itself is nice and smooth but randomly the engine will miss and either just stutter and recover or shut down. The engine will restart without issue. When the motor misses I also hear a FSSt type noise which lasts less then a half second. The sound is like a soft release of air. (not a fart)
History
I ran the motor over the rocks about 2 years ago and ended up replacing the lower end with a unit from a 1977 evenrude 55 HP unit.
I rebuilt the carbs and bypassed the VRO and now use mixed fuel at 50:1
Once this work was finished the motor ran and I never heard the descibed miss but the idle was awful and the unit stumbled when accelerating.
I went to work syncing the carbs which addressed most of the poor idle and acceleration issues. I decided to decarb the motor and change the plugs. I used Sea Foam. First with the prescribed 1 litre gas mix and ran the boat at high idle around the lake till that was used up. I then sprayed sea foam into the carbs with the boat running until it almost stalled. Then another hi speed run around the lake. I did this 3 or 4 times and then poured a few teaspoons into each cylindar and let sit for an hour. Once more run around the lake and then replaced the spark plugs and gaped to .30.
This is when the miss started to appear. I thought it may have been the plugs so I replaced them with another set and still have the problem. The miss is random and I can go an hour without seeing the problem. Outside of the miss the motor runs like a swiss watch. Much better then it ever has.
In reading I wonder if the decarb may have dislodged some dirt that is now sitting in the reeds. The reed area is a mystery area that I know nothing about.
I'm a tad confused with spark plug gaps as older documentation states a .20 gap and new stuff lists .30.. I have also see references to using .40 . (reduced fouling ?)
I do have a basic knowledge of the electronics and fear something is failing but only for a second before recovering. I'd hate to try and find a random failure like that with an ohm meter.
The compression is good as it was balanced at 105 prior to the seafoam and 125 after.
I have looked for loose connections and broken wires.
Any suggestions as to where you think I should be going with this would be appreciated. I may have missed something obvious and need to step back and refocus.
Many Thanks
Hazard
I have an odd problem with my 1986 Johnson 40 HP. The engine has a random miss that only appears at low RPMs and mostly during idle. The idle itself is nice and smooth but randomly the engine will miss and either just stutter and recover or shut down. The engine will restart without issue. When the motor misses I also hear a FSSt type noise which lasts less then a half second. The sound is like a soft release of air. (not a fart)
History
I ran the motor over the rocks about 2 years ago and ended up replacing the lower end with a unit from a 1977 evenrude 55 HP unit.
I rebuilt the carbs and bypassed the VRO and now use mixed fuel at 50:1
Once this work was finished the motor ran and I never heard the descibed miss but the idle was awful and the unit stumbled when accelerating.
I went to work syncing the carbs which addressed most of the poor idle and acceleration issues. I decided to decarb the motor and change the plugs. I used Sea Foam. First with the prescribed 1 litre gas mix and ran the boat at high idle around the lake till that was used up. I then sprayed sea foam into the carbs with the boat running until it almost stalled. Then another hi speed run around the lake. I did this 3 or 4 times and then poured a few teaspoons into each cylindar and let sit for an hour. Once more run around the lake and then replaced the spark plugs and gaped to .30.
This is when the miss started to appear. I thought it may have been the plugs so I replaced them with another set and still have the problem. The miss is random and I can go an hour without seeing the problem. Outside of the miss the motor runs like a swiss watch. Much better then it ever has.
In reading I wonder if the decarb may have dislodged some dirt that is now sitting in the reeds. The reed area is a mystery area that I know nothing about.
I'm a tad confused with spark plug gaps as older documentation states a .20 gap and new stuff lists .30.. I have also see references to using .40 . (reduced fouling ?)
I do have a basic knowledge of the electronics and fear something is failing but only for a second before recovering. I'd hate to try and find a random failure like that with an ohm meter.
The compression is good as it was balanced at 105 prior to the seafoam and 125 after.
I have looked for loose connections and broken wires.
Any suggestions as to where you think I should be going with this would be appreciated. I may have missed something obvious and need to step back and refocus.
Many Thanks
Hazard