When my cousin gets his banshee out and ready to ride, it has always been bad about fouling plugs why is that. He cobbs the crap out of it , its not like he dont blow it out good or anything it just does it every now and then. i have rode with a few that has not had the same trouble whats the deal

sorry about the double post hit the enter key and there it went

 

Could be his oil to fuel ratio , Old fuel , Low compresion , Rich idle circuit dirty air filter , to cold of plug , On And on and on .
Hard to say with out knowing a little more about the bike