95 112 spl poor compression #s

[66 joe]

after running boat for first time in 2 years, motor seemed to develop a miss and wouldnt go above 3000 rpm.
compression tested all cylinders at 120psi, except for 1, which was 100,
Went through rebuild 2 years ago. My mechanic claimed probably lean carb condition and overheated.
What should be my steps? pull head on bad side? hopefully head gasket, I dont know what else would cause
lower compression on 1 cyl. Thanks, Joe

 

[BonairII]

Re: 95 112 spl poor compression #s

I would change the head gasket and go from there.

Low compression could be caused by a sticking ring. I know motor was rebuilt recently, but maybe a ring is gunked up.

A "miss" could indeed be the so-called bad cyl running lean.

Probably a good time to pull the carb feeding that cyl and check it out(and rebuild it).

 

[66 joe]

Re: 95 112 spl poor compression #s

I pulled plugs and squirted some oil in the cylinders. I can manually turn flywheel with ease, (with no plugs) piston top looks good,
But when I install plug on bad cylinder and manually turn flywheel, I can hear air leaking somewhere upon compression.
I know , time to pull head. Other cylinders are real tight with plugs installed, but not # 1.
What should I be looking for?

 

[AEROCOOK]

Re: 95 112 spl poor compression #s

The air leaking sound could be compressed air going by the rings, especially if you have a stuck ring. Before tearing into it I think I'd do a decarb on it and see if the compression comes up on the low cylinder.