1992-1998 Kawasaki PWC Jet Ski Service Repair Manual., Page 56Get this manual
CRANKING SYSTEM the wear will be normal and in the case of pre-ignition, will actually cause the meltOverheating and are usually caused by overadvanced timing, detonation from using too-low rating fuel, an excessively lean airfuel mixture, or problems in the cooling system 5-9
to ground inside the shellT condition may also caused by ignition problems which prevent high-tension pulse be delivered the spark plug
Rich Mixture: black, sooty condition on both the spark plug shell and the porcelain is caused by excessively rich airfuel mixture, both at low and high speedsThe rich mixture lowers the combustion tempera so the spark plug does not run enough burn off the depositsDeposits formed only on the shell is indication the low-speed airfuel mixture is too richA high speeds with the mixture, the in the combustion chamber is high enough burn off the deposits on the insulatorToo Cook insulator, with very deposits, indicates the plug is running too coolThis condition be caused by low compression or by using spark plug of the rangeIf this condition shows on only plug is usually caused by low compression in cylinderIf both plugs have this appearance, the is probably due to the plugs having too-low range