I have a KX500 '86 that I have had rebored and a new piston kit put in. It started the first couple of times, now it won't start at all. Prior to rebuilding motor I always had trouble starting it, but eventually it would start, probably because i could kick it over faster due to less compression. The piston and rings and cylinder are still ok, the electrics have been checked and are ok too, carby and air filter are clean and reeds are fine also. There's no evidence of fuel mixture on the flywheel side crank seal or blowing white smoke ( when it was going). The flywheel woodruff key is ok and there's no movement and the timing is set at standard. Someone told me that the big end bearing could be worn in a spot where the piston reaches TDC and altering the timing. Could this be true? Any help would be much appreciated thank you.