1999 Ski-Doo Factory Shop Manual Volume Three, Page 85Get this manual
Section 03 TROUBLESHOOTING Subsection 05 (ELECTRICAL SYSTEM)
SYMPTOM CONDITION TestInspection
FOULED (BLACK) SPARK PLUG TIPNORMAL USE1Check carburetor(s)aCarburetion is too richAdjust according to specifications (refer to TECHNICAL DATA 10)2Check injection oil consumptionaInjection pump flow is too highAdjust according to specifications or replace3Check oil qualityaPoor oil quality that creates depositsUse BOMBARDIER-ROTAX injection oil4Check engine compressionaLeaking piston ring(s)Replace