1987 mercury outboard 60hp loss of power

[mtjesse]

I have a 1987 that use to take about 15 minutes to warm up. Once warmed up engine ran great about 35mph . The other day I took the kids out to have some fun on the tube after 15 minutes engine was running mint. I ran it for about 40 minutes and the engine started running like it would when I first started it. Now the boat won't go faster then 20mph. Its starts great but wont go faster then 20mph. It seems to me like its only running on 2 cylinders. The moter is a 3 cylinder. What should I check first to trouble shoot? Has this happened to anyone else? If so what did you do to fix it. Any info would be helpful.
Thanks

[mtjesse]

I just did a compression test and one cylinder has lower compression then the other two. Does anyone know how big of a job it is to replace the rings on this engine. My next question is will it hurt the engine running it like this?

[1nebel0]

You don't say how much lower...while it can be low it shouldn't have had the effect on your speed by that much unless you have a dead hole... state the numbers....Did you loose spark on a cylinder..need to rule that out as well as possible fuel issue...

[mtjesse]

Two cylinders at 135 the third at 115. I had the boat out yesterday fishing and ran at idle speed trolling for 15 minutes then third cylinder kicked in.

[RaScLeS]

you have a wiring issue as well when it kicks out or "while it warms up" trouble shoot the plugs by checking for spark. good luck, I know my merc when it works good can holeshot without even warming up for 2 minutes

also reccomend seafoam deep creep mystery oil any of that stuff in the cylinder with the motor tilted up for a day or so and re compression check

[PHE]

There is a decarb procedure in the FAQ. I would follow that procedure and see if it looses the rings up first. Seafoam is great stuff for that. I do it a little different. Every 100 hours or so, I put Seafoam in a spray bottle. Warm up the engine. Put it on a fast idle. Then spray into the carb throats alternating between them until the motor finally dies. Then let it sit for 15 minutes, start it, it will smoke like crazy for a few minutes. Then repeat it an couple more times until it doesn't smoke as bad when you restart it. Then do another compression check.

Also sounds like your loosing spark on a cylinder.

[mtjesse]

The sea foam worked great but I am still having issues with the top cylinder not getting spark all the time. When I start the boat no spark for 5 to 10 minutes in top cylinder. Once boat warms up it runs mint. I pull the tube around the lake for 30 to 40 minutes and lose spark in that cylinder again. I have checked the coils and plug wires and they are good all other electrical connection look good no corrosion or rust. Any ideas?

[mtjesse]

I still need help?