Compression

[reload]

What would be the lowest compression that a 15hp johnson would run? Seems like it runs on both cylinders til about half max rpm, then one cylinder seems to stop firing.

 

[DCC]

Re: Compression

sounds like carb problem if rings are wore they will run better the more rpm because air has less time to pass rings before it is exausted also your carb has 2 jets 1 for low end and one for top end i would check main jet in carb but seems like most motors will run ok around 90 to 100 psi maybee just low on power hope that helps

 

[F_R]

Re: Compression

If just one cylinder stops firing, look for an ignition problem. Especially one related to the throttle position. Don't ignore the spark plugs...try some new ones.

The carburetor feeds both cylinders equally, unlikely that is the problem.

I agree the compression is not likely to be the culprit. That would show up more at starting and idle speeds.

What year is your 15? Any possibility it is getting water in the cylinder? A leaking head gasket will do that, AND lower the compression reading.

 

[asdasc]

Re: Compression

Or a cracked coil. It could start shorting one of the coils at higher speeds.

 

[kenmyfam]

Re: Compression

To start the ball rolling what is the compression ???? Symptoms do not really relate to a compression issue at this point though. Ignition most likely as stated already.