Fouled Plug

To find a bad valve, you should then do a leak down test after the compression test.

You will need to buy a leakdown tester and have a source of compressed air. Then follow the instructions on the leakdown tester.


Basically, you put the cylinder at TDC and then pressurize it. Then "hold" the pressure and see if it leaks. If a valve is leaking, you can hear an intake valve leak through the carb, and exhaust valve leak through the tail pipe, and any ring leaks through the crank case.