missing merc

[Stoneman]

I have an 89 115hp merc that sometimes won't kick in all cylinders when given full throtle, she will idle and putt along just fine then when given full the other two won't kick in, then after a bit of high speed idle in neutral they will..... Question, is the low RPM module the problem?

[luckey]

Better do a compression test. I think you may have a bad piston. No compresion, no firing. After a while oil seals the bad piston and away you go.

[Jeremy airjer W]

If you had bad compression wouldn't you feel the misfire more at idle and the engine would smooth out at the higher RPMS. This seems to be doing the opposite. Smooth idle but misses at higher RPM. If this was a vehicle I think I would be looking at ignition. For example, bad ignition wires can cause no symptom at idle. When accelerating (putting more load on the engine) the bad wire will become apperrant as an engine misfire. Once you have accellerated to your cruising speed (simular to idle - much less load then acceleration) the misfire goes way.

You could try checking spark. I assume this has spark plug wires so you could try spraying the wire with water to see if there leaking.

By no means do I claim to know anything about this topic so I could be way off base!!

[marine_man]

I'd do a compression test to verify that all of your cylinders are good...

Ignition is also a very good possibility... one coil pack usually runs two cylinders, so it could be that, or if your engine has one carb for two cylinders it could be a piece of debris stuck in the high speed jet...

marine_man