2003 Ski-Doo REV Series Factory Shop Manual, Page 209Get this manual
Section 06 ELECTRICAL Subsection 03 (SPARK PLUGS)
DISASSEMBLY
First unscrew the spark plug turnClean the spark plug and cylinder head with pressurized air, then completely unscrew
WARNING
Whenever using compressed air, always wear protective eye wear
CAUTION: Severe engine damage might occur if wrong heat range plug is usedA plug that would be too hot will result in overheating and pre-ignition, etcA plug that would be too cold will result in fouling (shorting the spark plug) or may create carbon build up which can heat up red-hot and cause preignition or detonation
HEAT RANGE
The proper operating temperature or heat range of the spark plugs is determined by the spark plug ability to dissipate the heat generated by combustionThe longer the heat path between the electrode tip and the plug shell, the hotter the spark plug operating temperature will be and vice-versa, the shorter the heat path, the colder the operating temperatureA cold type plug has relatively short insulator nose and transfers heat very rapidly into the cylinder headSuch plug is used in heavy duty or continuous high speed operation to avoid overheatingThe hot type plug has longer insulator nose and transfers heat more slowly away from its firing endIt runs hotter and burns off combustion deposits which might tend to foul the plug during continuedidle or low speed operation