1989 Ski-Doo Repair Manual, Page 379Get this manual
Section 04 ELECTRICAL SYSTEM Sub-section 03 (SPARK PLUGS)
DISASSEMBLY
First unscrew the spark plug one turnClean the spark plug and cylinder head with pressurize air then completely unscrew
FOULING
Fouling of the spark plug is indicated by irregular running of the engine, decreased engine speed due to misfiring, reduced performance, and increased fuel consumptionThis is due to loss of compressionOther possible causes are: prolonged idling, or running on too rich mixture due to faulty carburetor adjustment or incorrect fuel andor fuel mixingThe plug face of fouled spark plug has either dry coating of soot or an oily, glossy coating given by an excess either of oil or of oil with sootSuch coatings form conductive connection between the center electrode and ground
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 to the plug shell, the hotter the spark plug operating temperature will beand inversely, the shorter the heat path, the colder the operating temperature will beA "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 prolonged idle or low speed operation