1999 Ski-Doo Factory Shop Manual Volume Three, Page 209Get this manual
Section 06 ELECTRICAL Subsection 03 (SPARK PLUGS)
SPARK PLUGS
NGK SPARK PLUG
All Models
NGK SPARK PLUG NUMBERING SYSTEM
Bombardier uses NGK brand spark plugs on all its snowmobile modelsThe heat range identification system is: Low number High number hot plug cold plug