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I have a 1991 Mercury 75HP outboard - ser# 0C259832. I need help determining what is failing if you can help.
Motor starts and idles great. When throttling-up, engine runs great... then 5 or so minutes into run engine dies (a sound similar to the ratcheting sound the prop gears make if motor was left in gear while boat was still in motion - this noise starts to climb in volume at the motor looses power and dies). This sound is produced regardless of engine speed or boat speed, even at low revs. The motor will restart immediately. Once underway, the engine will die shortly thereafter - 3-5 minutes - it seems to be a heat build-up issue in the electronics.
Before the motor started to die (with noise), I was having problems with the motor seemingly loosing a cylinder (loss of power) - this was intermittant. After cleaning carbs, rebuilding fuel pump and adding water seperator unit the motor just dies now...
I have also checked the thermostat to make sure it wasn't stuck - I thought maybe it was getting hot causing detonation before the buzzer would go off.
The sound that I try to describe above was noted to be possibly an electrical arcing sound, but I have not yet removed the flywheel to see if there is any discoloration, blistering, carbon deposits, etc. I have fully inspected all high voltage spark plug wires and coils for tell-tail carbon marks, but have found nothing.
Compression is 110 across all cylinders, I have spark on all three cylinders.
I have swapped-out the switch box with a known good unit and the problem is still there - possibly the trigger or stator?
Just for conversation... Maybe the noise is from the gears... it only makes the sound as the engine just starts to loos power - I can almost hear the noise before the power starts to die-off. I'll take ohm reads on the stator, then heat the flywheel to see if I get resistance changes throught the stator.
Does anyone know of the proper ohm readings that I should get off the Mercury RED stator... my service book covers 9 & 16 amp stators with differnt stator part numbers listed (other than various look-ups on the web, I can't verify if I have a 9 or 16 amp stator). My current stator 398-832075A3 is listed as a 16 amp unit.
Dan-
I've got a red stator with problems similar to yours...
My stator has grn/wht, wht/grn, a blue (appears to be to the coils), two yellows and there may be another... Too lazy to go look right now, but i'll tell you if you've got between 600 and 700 ohms on the grn/wht and wht/grn that the stator "checks" good. Mine checks good but still kills at anything around 3/4 throttle. If you have a blue wire, I'd check that from there (Stator-side) to ground. CDI says it should be open "OL" but I actually read some resistance... I'm leaning toward this not being good. I haven't figured my deal out yet, but figured I'd share my issues and findings, maybe it'll help my karma...
If you haven't already resovled your problem, I can say I had a similar problem this year and it turned out to be that i had a crack in my oil line coming of the fuel pump. Once fixed the problem stopped.
75HP Mercury Dies with Strange Noise
Linear Mode
