Compression Check: Testing and Inspection

CAUTION: Remove fuel pump Electronic Control Module (ECM) from left side electrical center.

To determine if the valves or pistons are at fault, a test should be made to determine the cylinder compression pressure. When checking cylinder compression, the throttle and choke should be open, all spark plugs removed, and the battery at or near full charge.


The lowest reading cylinder should not be less than 70% of the highest and no cylinder reading should be less than 689 kPa (100 psi). This should be done with four "puffs" per cylinder.


NORMAL
Compression builds up quickly and evenly to specified compression on each cylinder.

PISTON RINGS
Compression low on first stroke tends to build up on following strokes but does not reach normal. Improves considerably with addition of oil.

VALVES
Low on first stroke does not tend to build up on following strokes. Does not improve much with addition of oil.

Use approximately three squirts from a plunger type oiler.