1997+ Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-826148R2, Page 27Get this manual
CAVITATION avitation is caused by water vapor bubbles forming either from sharp edge or angle on the ge ar case or from an irregularity in the propeller blade itselfThese vapor bubbles flow back and collapse when striking the surface of the propeller blade resulting in the erosion of the propeller blade surfaceIf allowed to continue, eventual blade failure (bre akage) will occur D etonation usually can be prevented if: 1The engine is correctly set up2Diligent maintenance is applied to combat the detonation causes
DETONATION etonation in 2-cycle engine resembles the "pinginghe ard in an automobile engineIt can be otherwise described as tin-like "rattlingor "plinkingsoundD etonation is an explosion of an unburned portion of the fuelair charge after the spark plug has firedD etonation cre ates severe shock waves in the engine, and these shock waves often find or cre ate we akness: The dome of piston, cylinder he adgasket, piston rings or piston ring lands, piston pin and roller be aringsA few of the most common causes of detonation in marine 2-cycle application are as follows: ver-advanced ignition timing Use of low octane gasoline Propeller pitch too high (engine PM below recommended maximum range) Le an fuel mixture at or ne ar wide-open-throttle Spark plugs (he at range too hotincorrect re achcross-firing) Inadequate engine cooling (deteriorated cooling system) ombustion chamberpiston deposits (result in higher compression ratio)51115