This past Saturday we ran with another pair of Ski-Doo sleds a 500 and a 370 - both fan cooled. The 500 fouled the PTO side plug twice during the day. We have not had much problem with fouling plugs on our sleds so I was hoping for some insight for why that might have been a recurring issue on that sled. Plug was NGK BR9 EYA, temps in the mid 30s, non-ethanol fuel. Sled has single 36 or 38 mm Mikuni carb non-powerjet.