Check that the battery is charged. Under no-load conditions there must be a charge of at least 12.5V measured at the terminals.
Start the engine and allow it to warm up. Wait until the electric cooling fan switches on at least once and then switch off the engine.
Open the throttle fully.
Remove the spark plugs.
Warning! To prevent sparks, earth the spark plug cable.
Screw the adapter into the spark plug hole of the cylinder to be tested.
Turn the engine over using the starter motor until the pressure reading stops rising.
Check the compression of both cylinders.
- Standard compression: 9-11 bar
- Minimum compression: 8 bar
- Maximum permitted compression difference between cylinders: 2 bar.
Excessively high compression readings indicate the following:
- Deposits in the combustion chamber.
Low compression readings indicate:
- Blowing cylinder head. Gas leakage between head and cylinder.
- Worn valve seats.
- Bent valve stems.
- Incorrect valve clearances.
- Worn cylinders or piston rings.