Alright, I can say I am truly stumped. and I am asking for help. I have an 03 Yz 450F and the rear intake valve is stuck and it can't go down(with the spring on). it is the intake valve that is closest to the kick-starter. But when I take the spring out the valve moves freely( pretty much no resistance). the valve cap/ bucket has no scrape marks on it(so it's not rubbing). Can anyone help me? They are also new valves the head just came back from a shop(got the guide reamed out). I also checked the valve and it is not bent. Any help?