2004-2006 Honda FourTrax Rancher TRX350TE/TM/FE/FM Service Manual, Page 359Get this manual
IGNITION SYSTEM
TROUBLESHOOTING
Inspect the fo ll owing before diagnosing the systemFau Ity spark lugLoose spark plu cap or spark plu wire connectionsWater got into the spark plug cap (Leaking the ignition coil secondary voltage)