My 08 yfz 450 ran and started cold or hot flawlessly since new,, Then one day it started right up then stalled. At that point I couldent get it started again for the life of me. So I Took it too a shop and they said my Timing Chain jumped timing. They put new timing chain in w/tentioner, since then it's very difficult to get it started when it's cold. Once it's hot it'll fire right up no problem. I also noticed the idle is rough as well while it's cold. Hard to keep it running. Once it's hot it starts an idles fine. Other then that it runs like a raped ape!

 

Could be lots of things, but the two things I would look at first are valve lash and double check the cam timing.

 

Spot on. Your valves are probably out of spec and in need of reshimming. The timing could also be off a bit. Worst case scenario is a valve got a little damaged when the chain jumped and the shop didn't catch it. Valve lash and timing are a cheap and easy fix, and you need to know that stuff is right before moving forward.

 

Good calls,, I was thinking Carb maybe.. But Y'all are right, I have heard valve trouble after a timing issue. Some cases really bad. Things getting all banged up in there if the chain was to break. So I'll have valves etc checked asap. Sucks tho cause they should have checked all that to be sure anyway while it was all opened up.

 

But they won't have you bring it back, and be able to extort more money from you, if they check everything properly!.

 

so I took it to another shop,,, The guy i used to go to with any problems. He said it prob wasnt the timing at all. WTF! He said if the chain jumped timing, 1-2 teeth etc, id have serious engine damage no question, well i do wanna beleive that cause it does run when its hot. So cant be too damaged. Right? Runs dam good! I hope it is just something minor.. Valve adjustment like yall say. see what happens...

 

I don't want to start a big thing, but one tooth will not run into interference.
YouTube - YFZ450 cam mod Ever hear of a cam mod? You might show your mechanic this video.

 

your valves are to tight.

 

Thanks guys,, yea I took my YFZ in the shop, did a compression test yesterday,, air was pouring out of the Intake. So prob looks to be intake valve? So they state just needs valve adjustment/shims. Sound right? See what happens!