1987 50 hp 3 cyl 2 stroke

I have an 87 50 hp yamaha that has been nothing but trouble.

After blowing a #1 piston, and having the head re-built, I have the following symptom:

When the motor is under torque (ONLY- it will run indefinitely, even at high rpm, when not in gear and in the water) the motor powers down and stalls after a few minutes at anything higher than about 2000 rpm. Higher rpms=faster power down. Worse in rough water.

I have had it tank tested by a reliable dealer, who said it apears that when the motor is under torque at high rpm, the flywheel drops a bit and bumps the coil, causing the power down.

He suggested MAYBE the main bearing, but no guarantees. I've talked to a couple engineers and small motor mechanics, who said, yeah, could be.

I want to minimize my expense, and I'm angry at this motor. I'm going to try to tear it down myself, and replace the main bearing.

Does anyone have similar experience? Any wise words of advice?

[boats.net]

No I haven't had that problem. Check top bearing for play, see if can move flywheel from side to side. Remove flywheel and see if is hitting coils.

OK, no play in the flywheel, very tight. Removed the flywheel, perhaps very slight "scorching" of white tape on one coil.

Is it possible this could be a sensor problem, ie, oil injection sensor or temperature sensor? How could I test this? I have the Seloc repair guide, but there seems to be many. many possible causes. I'd rather not tear down to the main bearing.

[boats.net]

You are right that it could any number of things. Check compression, look for air leaks on intake, crankcase halves, crankshaft seals. Carb or sync problems or igntion problem.