YZ450F Not Runing too good after Rebuild?

[martis_d]

Not running too good after top end rebuild and new cam chain. i put a cp piston in it and upped the compression a little and done all the valves after finally putting it back together it will not kick start, had to push start it down a hill(not fun)then i blead the oil line to the head and after that it ran for not even 5 minutes, it then snuffed after i tried to crack throttle. after running it still would not kick start(***), driving me nutz. any help please ppl.

cheers

Mad Dog

[TIG88]

Double check timing and valve clearence.

[knuckleduster271]

Those 5 valve motors, two of the valves look alike but are a hair different in size, you may have gotten these mixed up if you took the valves out

[martis_d]

It Ran, the valves there is no way they got mixed up at all.

will be going through a few things starting with the basics carby service, new spark plug then dig deeper and go through the timing. i was so sure with the cam chain timing but will be tripple checking it again.

[FEAROFRUNNER]

I just did a rebuild on my 426 with pretty much everything you descriped minus the hi-comp pistion. It was hard to get started also, not hard kicking just didn't want to fire and was that way untill i got about 5 hrs on the motor. If I understand right, when a brand new motor is being broke in, the compression isn't the greatest untill those rings seat. If everything sounded ok when you did get it started then i would say try it again.

[spark250]

As mentioned above I think you need to check your timing and valve clearances.

[TIG88]

I just did a rebuild on my 426 with pretty much everything you descriped minus the hi-comp pistion. It was hard to get started also, not hard kicking just didn't want to fire and was that way untill i got about 5 hrs on the motor. If I understand right, when a brand new motor is being broke in, the compression isn't the greatest untill those rings seat. If everything sounded ok when you did get it started then i would say try it again.

Your rings will seat well within the first several minutes of running. This is assuming your running it hard and under a load. Deceleration is key here too.

My bike was never hard to start after a rebuild.

[martis_d]

I looked into it and found the cam timing out by one tooth on both cams, i fixed that then broke the plastic and of the hot start choke cable going into the carb and lost the spring......gr.. orded new ones and have to wait to fire it up.