ok so i was riding my bike pretty hard a lot of high revs. and i heard a funny noise come out of my engine so i backed off and grabbed the clutch, when i came to a stop and tried to start my bike up again. there was just nothing and there was very little effort required to kick it over. so i got my bike back to my shed and tore the engine down and discovered there was a peice of the piston missing. the piece was about 4-5 cm long, 1-2 cm wide and about 1cm deep, it went from the top of the piston down to the ring. it is a fairly sizable piece. oh and it is right in front of the exhaust port. any ideas as to why this happend? i run 98 octane premium unleaded, FMF fatty, power core II silencer and jetting is as per FMF's specs.