1985 90hp mercury compression problems

[Webb317]

I bought a 1985 cheetah 166 with a 90hp mercury and after taking it out several times it doesn't run with full power
When gas it all the way. After reviewing the repair service records, I found that it was documented that this motor has borderline compression. My question is what needs to be done to fix this problem?

 

[JB]

Re: 1985 90hp mercury compression problems

What is "borderline" compression?

 

[Silvertip]

Re: 1985 90hp mercury compression problems

Restoring engine compression can take two paths. 1) Compression may be low because of carbon buildup in the ring lands (the grooves the piston rings sit in) which prevents the rings from sealing combustion pressure normally. The solution for that is to perform a "decarbonization procedure" (use the SEARCH feature) which should bring compression up. In very serious cases the engine may need to be disassembled and new rings installed provided the cylinder bores are ok. 2) Compression may be low because the engine is simply worn out and the rings can no longer seal properly, or there is serious cylinder scoring or other issues. Corrective action requires a total engine rebuild or power head replacement.