1986 Ski-Doo Factory Shop Manual, Page 373Get this manual
Section 04 ELECTRICAL SYSTEM Sub-section 03 (SPARK PLUGS)
DISASSEMBLY
First unscrew the spark plug one turn Clean the spark plug and cylinder head with pressurize
FOULING
Fouling of the spark plug is indicated by irregular running of the engine, decreased engine speed due to misfiring, reduced performanceand increased fuel consumptionThis is due to loss of compressionOther possible causes prolonged idling, running the engine with the choke on (Formula Plus only), 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
air then completely unscrew
HEAT RANGE
The proper operating temperature or heal range of the spark plugs IS determined by the spark plug's ability to dissipate the heat generated by combustion, The longer fhe heat path be'tween the electrode lip to the plug shell, the hotter the spark plug operating temperature will be and inversely, the shorter the heal palh, the coJder the operating temperature will be