1998-2004 Honda Foreman 450 factory service manual, Page 138Get this manual
CYLINDER HEADCYLINDERPISTON
CYLINDER COMPRESSION TEST
If the engine must be running to do some work, make sure the area is well ventilatedNever run the engine in an enclosed areaThe exhaust contains poisonous carbon monoxide gas that may cause loss of consciousness and may lead to deathRun the engine in an open area or with an exhaust evacuation system in enclosed areaWarm up the engineStop the engine and remove the spark plugInstall compression gaugeOpen the throttle all the way and crank the engine with the starter motor until the gauge reading stops risingCompression pressure: 539834 kPa (5.58.5 kgfcm2, 78'21 psi) at 450 rpm If compression is below than the standardloosen the exhaust valve lock nut and turn the adjusting screw 1-12 turn and recheck the compressionCompression pressure: ',226',442 kPa (12.514.5 kgfcm178206 psi) at 450 rpm Low compression can be caused by:Blown cylinder head gasketImproper valve adjustmentValve leakageWorn piston ring or cylinder High compression can be caused by:Carbon deposits in combustion chamber or on piston head