2011 KX250F won't idle
 

So I have a 2011 Kx250f. Used it as my race bike. changed the oil and oil filter every weekend and took excellent care of it. One race at 140 hours I blew the oil ring. So I decided to replace the whole top end. When we got the seats cut in the head, it burnt the cylinder and cracked it. so we bought a new cylinder and seats then ever since then it wont idle. we replaced the timing chain, air temp. sensor, we just put in all new bearings, and still won't idle. Also, it gets hotter than it is supposed to and is hard to start unless the idler is pulled out. Any info to get it fixed would be appreciated.