1979 Ski-Doo Supplementary Shop Manual, Page 134Get this manual
SECTION 05 SUB-SECTION 02 (SPARK PLUGS )
SPARK PLUGS
SPARK PLUG NUMB ER IN SYSTEM
Bosch has introduced new numbering code for its complete line of spark plugsThe new code is shorter, therefore easier to useThe following charts will assist you in making the change-over easily and effectivelyIMPORTANT: The new code has different heat range identification systemHigh number hot plug Low number _ cold plug