1978 Ski-Doo Shop Manual, Page 226Get this manual
SECTION 04 SUB-SECTION 04, (IGNITION TIMING)
EDGE GAP VERIFICATION
By following either of the procedures mentioned herein the edge gap will automatically be adjustedHowever, if the edge gap is to be verified, proceed as follows: From timing marks, rotate magneto clockwise 14 of turnHold advance mechanism centrifugal weight in the open position (toward magneto rim) then slowly turn magneto back counter-clockwise until timing light fluctuates or until tone signal sound level varies
At this point check the distance between pole shoe trailing edge and magnet (edge gap), with strip of cardboard of appropriate width(Refer to the following table Engine type Edge gap 7-11 mm (.275430") 5-8 mm (,200.315")