1981 Ski-Doo Shop Manual Supplement, Page 49Get this manual

SECTION 03 SUB-SECTION 03 (IGNITION TIMING)
IGNITION TIMING
For the folowing 1981 engine types:
247-277 377-503

refer to the 1980 Bombardier Snowmobiles Shop Manual (section 03-03)For the folowing 1981 engine types:

• ATV
• Jet Ski
• Outboard Motors
• Personal Watercraft
• Snowmobiles
• Stern Drives