Low compression

[searayray]

Just got an 1988 Johnson 70 HP have not tested in the water yet runs on the hose OK compression is equal in all three but at 75lbs. I assume this is low. I could see if only one piston was producing a low number but all three what could cause this?

 

[xtraham]

Re: Low compression

confirm the compression gauge you are using, check @ operating temp., if it is still low decarbon engine w/seafoam and seafoam deep creep, those engines where lugged alot and will build carbon.

 

[Dhadley]

Re: Low compression

The gauge could be showing a bit low, the cranking speed may be slow, maybe it didn't turn over enough times, which head it has, etc. There are lots of variables. That's why OMC never gave a specific number but rather a range.

I'd have to agree with X -- do a good decarb and test again. I'll bet you're OK.

 

[clanton]

Re: Low compression

If your gauge is good, 75 is to low, also check the crankcase pressure.