Although I ride a thumper, my girlfriend rides a 2-stroke KX100 which loves to foul plugs inconsistently......bike starts first kick, runs great for hours, but shut it off then try to to start it......fouled again! Took it in to a local race tech....his reply change oil mix......did it....fouled again......tried hotter plugs......fouled again......changed jetting clip adjustment to make it leaner......fouled again.......good synthetic leaner mix.......fouled again.......perhaps this bike is a four-stroke cause we tried everything short of removing oil from the picture entirely.....................................................................frustrated!