[bikegod66]

i am thinking about buying a 1985 40 hp yamaha, the compression checks at 80 for all 3 cyclinders . is this average compression for a yamaha ?

thanks to all

[steelespike]

That is a little low general rule of thumb for outboards is 100 PSI and within 10% between cylinders.It is good that they are even.If its been sitting a spell it might be low.You could squirt a little oil in the cylinder and see what you get.Spin it till the gauge stops going up.

[deejaycee_2000]

i agree, a good compression is about 100 psi and a great one 120psi, 80psi is ok for such a old motor, and after a rebuild should you decide to do one, would make that motor as good as new ......