Make sure the transmission is in neutral.
Warm up the engine to normal operating temperature.
Stop the engine, disconnect all spark plug caps and remove one plug at a time
Install the compression gauge into the spark plug hole.
Open the throttle all the way and crank the engine with the starter motor. Crank the engine until the gauge reading stops rising. The maximum reading is usually reached within 4-7 seconds.Compression should be 171 psi/400rpm
If compression is high, it indicates that carbon deposits have accumulated on the combustion chamber and/or the piston crown.
If compression is low, pour 3-5 cc of clean engine oil into the cylinder through the spark plug hole and recheck the compression.
If the compression increases from the previous value, check the cylinder, piston and piston rings.
If compression is the same as the previous value, check the valves for leakage.
It is a recommended to use an anti-seize compound on the sparkplug threads when removing and replacing sparkplugs to prevent the plugs from seizing in the heads.