John F.

I'm planning on checking out 2 boats this weekend that I'm interested in. One has a '97 Yamaha 150, the other a '94 Yamaha 200 that was recently rebuilt (I know, I know). I plan on going for a ride to see how they run, and then if I can work out a deal, do a compression check and look at the lower end oil.

I haven't done this in a while. As I remember, its ignition off, throttle open, crank and check. What numbers should I see? I remember the 10% variation rule, but is it something like 115 psi on a 2-stroke?

Thanks.

A1 Outboard

You don't need to open the throttle on a 2 cycle motor as it is the exhaust port that allows air in and compression does not start until the top piston ring travels past the top of the port.

there are no compression numbers as that changes with cranking rpm, temp, amt. of oil in the cylinders, etc. All should be within 15# from the highest to the lowest.

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John F.

Thanks. Much appreciated.