ok a motocross bike should really be set up to tickover as it will go fora run by itself if you fall off it but nether the less they will have a tickover screw.if it wont tickover with the screw wound in then its going to be low on compression and needs looking at.the reason it cuts out when you put it in gear while its ticking over is because the clutch plates have bitten into the fingers of the clutch basket and the plate are not seperating when the engine is running as it will force them into the grooves and hold them together,so take the clutch out and either replace the basket or file the nibble mars out with a file until its flat on the side of every finger again you will notice one side is worse then the other thats beacuse one side drives and the other one is from engine braking remove them all though to make it nice again.its very common on mx bikes to see this problem.
adam bike doctor
June 2010
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