Johnson 85hp low compression on one cylinder.

[Lk40hp]

I have a 1978 Johnson Javelin 85hp. Compression is 116, 115, 115, and 100. The motor runs and works pretty well. Top speed of 37mph with a 17 pitch aluminum prop. Top rpm is 4500 even. Should I adjust the throttle linkage? Does it NEED a new ring kit or piston??? Should I just use it as is?

 

[JB]

Re: Johnson 85hp low compression on one cylinder.

No, it only needs routine maintenance, decarb to be specific. The OMC Manual says there should be less than 15% span. You are too close to that to panic.

Do a thorough decarb (see directions in Engine FAQs), then do another compression test by the method also found in Engine FAQs. Let us know what you get.

 

[Boss Hawg]

Re: Johnson 85hp low compression on one cylinder.

I have a 1978 Johnson Javelin 85hp. Compression is 116, 115, 115, and 100. The motor runs and works pretty well. Top speed of 37mph with a 17 pitch aluminum prop. Top rpm is 4500 even. Should I adjust the throttle linkage? Does it NEED a new ring kit or piston??? Should I just use it as is?

I'd do a good sea foam de-carb on it & check it again-
Looks like JB had his coffee first :laugh:

 

[Lk40hp]

Re: Johnson 85hp low compression on one cylinder.

I will do that and get back to you guys, thanks for the replies!