I have an '06 CRF250R and I recently rebuilt the top end. I was having trouble starting it because of a worn out valve. Now with a fresh top end (piston 13.5:1, new valve springs, new valves, stage 3 cam) it acts like the kicking stroke is severly short. When I kick and I get to the bottom of it's stroke the motor stops turning immediately. Has any one heard of the decompression arm not working properly? If I pull start it (with a 4wheeler), the bike cranks over with a quarter turn of the rear tire and runs incredibly strong. Any ideas?