2003 Ski-Doo ZX Series Factory Shop Manual, Page 72Get this manual
Section 03 TROUBLESHOOTING Subsection 02 (ENGINE)
4Check ignition timingaIgnition timing is too advancedAdjust according to specifications (refer to TECHNICAL DATA)5Check if there are leaks at air intake silencer andor engine crankcaseaLeak(s)Repair or replace6Check condition and heat range of spark plugsaMelted spark plug tip or inadequate heat rangeReplace
Liquid-Cooled Engines