1972 Ski-Doo Shop Manual, Page 204Get this manual
SPARK PLUG
ratio, or excessively advanced ignition may also give rise to pre-ignition
This is why Bombardier Ltd as result of exhaustive tests, specify spark plug which is the most favourable when operating the vehicle at full throttleHowever, when prevailing condi tions do not permit such operation, hotter plug (one heat range honer) can be installed to prevent possible foulingTo prevent piston failure, always reinstall standard plug for high speed operation(See Spark Plug Chart)NOTE: Bombardier-Rotax engines are equipped with Bosch spark plugs therefore, it should be remembered that Bosch spark plugs with low figure (W225T 1) is honer plug than spark plug with high figure (W260T1)CAUTION: Under no circumstances should a