First the piston needs to be 1/4" past top dead center on the compression stroke. That will get the cam off the compression release. Remove the breather hose from the carb and lock the crankshaft with a suitable clamp and pressurize the leakdown tester. The book says 60 psi but 15 psi is enough. Air leaking from the breather hose indicates bad rings, from the carb indicates leaking intake valve and from the exhaust indicates leaking exhaust valve. If air is leaking from both valves the piston in on the intake stroke not the compression stroke.
Rick, April 2007
