1971-1973 Arctic Cat Snowmobiles Factory Service Manual, Page 112Get this manual
ELECTRICAL Spark plug manufacturers vary the construction of the insulator to obtain spark plugs of different heat rangesThe various spark plug manufacturers have plugs in many sizes from which plug of the correct heat can be selected (see Spark Plug Chart, page 105)CAUTION: DO NOT sandblast, scrape, or in any way attempt to clean fouled or dirty spark plugsForeign particles may drop into the cylinder and cause severe engine damageOptimum engine performance is obtained with new plug of the proper heat rangebelowThis air gap setting has direct influence on every aspect of engine performance; starting, idling, power, acceleration, and top end speedEach spark plug must be gapped uniformly to insure optimum performance of the engine
Installation
Spark plugs must be installed properly to operate correctlyA new metal washer (gasket) should be used when plug is installedclean the gasket surfaceCAUTION: Do not allow any foreign matter to enter the spark plug hole when cleaning the gasket surface or when installing new plugFailure to observe this caution may cause internal engine damageThe spark plug should be tightened with torque wrench according to the spark plug manufacturer's torque specification