Warm the engine to operating temperature, then shut it off
Disable the ignition system and fuel system
Remove all spark plugs
Open the throttle fully
Thread a compression tester into the first spark plug hole
Crank the engine for several revolutions until the gauge stops rising
Record the reading
Repeat for each cylinder
Compare all readings to the manufacturer’s specification
Compare cylinder readings to each other
Add a small amount of oil to a low cylinder and retest if needed
Reinstall spark plugs, ignition components, and fuel system parts