1984 85hp force sputtering backfireing and dieing

[Fullforce]

Hi I really need help I bought a 16ft trophy bass boat a couple of months ago.the motor a 1984 force 3 cylinder 85hp with three seperate coils and two cdi boxes will only stay running with the throttle pushed forward a little.At idle it only runs for about a minute or so if that long.Then you hear motor come to abrupt stop with a chuffing sound.even at higher rpm you can hear the motor stumble.it will run chuff run chuff until you let off then it dies.At full wot it runs alright on the water but you have to push it into gear really fast or it cutts off.Very dangerous.I checked fuel filter and carbs for trash,replaced plugs,replaced coils,the sound appears to come from the third cylinder when I ran it with only first and second cylinder it ran without the sound.It seems to me that maybe the timing is off.If that is the case how do I go about timing it.It has timing mark on flywheel.I checked it at idle the mark on the flywheel was about an inch to the right of the mark on the motor.Can someone tell me how to time this thing.Thanks in advance

 

[steelespike]

Re: 1984 85hp force sputtering backfireing and dieing

Speaking generically.You could change the coils around to see if the problem follows the coil.<br /> Sometimes the run and cough at idle can indicate a lean condition.Whatever carb is involved with the problem cylinder may need to be cleaned.Be sure you dont shift it to much from a high idle as it will wear out the clutch dog.You could try a little choke to see if it helps the cough if the choke helps then it is lean.