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1986 115hp mercury 6 cylinder

B

blackdog1970

New member
Hello,
Looking for opinions on an issue that has arose. I lost power a few weeks back. My boat would get on plane but had much less power so I thought I had lost a cylinder. I replaced all 6 spark plugs and went back out. The boat ran great for 2 or 3 outings then the same problem has came back so I'm guessing the motor fouled another plug. I was told it could be a coil or possibly the stator. Please give me any advice on this issue. Thanks for yourtime.
 
I can not see , hear or feel your motor.---Need the facts to advise you.----The trouble shooting on an outboard starts with a compression test.----Report your numbers.-----Next is a spark check.---Good spark jumps a gap of 3/8" or more on each lead.-----And carburetors must be confirmed clean.----A restriction means less fuel and LESS OIL going into 2 cylinders !----And finally those motors need a new water pump impeller every 2 or 3 years.
 
racerone said:
I can not see , hear or feel your motor.---Need the facts to advise you.----The trouble shooting on an outboard starts with a compression test.----Report your numbers.-----Next is a spark check.---Good spark jumps a gap of 3/8" or more on each lead.-----And carburetors must be confirmed clean.----A restriction means less fuel and LESS OIL going into 2 cylinders !----And finally those motors need a new water pump impeller every 2 or 3 years.
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Racerone,
The compression on 4 cylinders was 120. One was 118 and one was 116.
Carbs were redone maybe 3 years ago. I think they are good but have noticed some fuel leaking. I don't see anything leaking when I pump the primer ball so I'm wondering if I'm getting fuel leaking abit when motor is raised up. I will check spark jump gap next. Also it is due for water pump kit. This will be 3rd year since last impeller service. Thanks for your reply.
 
blackdog1970 said:
Racerone,
The compression on 4 cylinders was 120. One was 118 and one was 116.
Carbs were redone maybe 3 years ago. I think they are good but have noticed some fuel leaking. I don't see anything leaking when I pump the primer ball so I'm wondering if I'm getting fuel leaking abit when motor is raised up. I will check spark jump gap next. Also it is due for water pump kit. This will be 3rd year since last impeller service. Thanks for your reply.
Click to expand...

Well I checked spark and had the 3/8" jump on all cylinders so I pulled the plugs next. When I pulled out #2 plug there was a small metal shaving on the electrode. I also looked is side the cylinder as best I could with a flashlight and it looked like a few small metal shavings on cylinder wall. So then I checked old plugs and found a plug with some small bits of metal on that electrode. A buddy that knows these old motors pretty well and said it's probably from the piston. He thought it may have been an over heating issue that may have caused it. He said to check compression again on #2 to see if it's still 120. Anyway that's the newest update. Thank you
 
If top of piston deflector is eaten away it is aluminum throwoff on plug. Either idle stabilizer is hooked up and bad or switchbox has bias circuit bad causing timing to be off on that cylinder.
 
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