yfz450 problems...

[HyBrid00benji]

I'm listing this add for a friend; I've been helping him work on it.

He has an 04' yfz, bone stock except for exhaust and air filter motor wise; just the other day he was riding through the field draggin against someone else. He went through 1st 2nd 3rd turing it hard, it backfired and cut off. All it will do now is spin over.

I thought maybe he sheared the flywheel key. I pulled the flywheel off and the key is fine, also the timing is perfect. No slack in timing chain. I thought maybe he floated the valves and bent them from turning it hard but its making good compression.

His plug is firing, atleast when we pull it out. But, when you pull the plug out it smells strong with gas after it has been spun over.

I'm kinda clueless, it backfires a little turing it over though... Maybe its got some wiring issues or could be the rev box, i honeslty don't know..

[HyBrid00benji]

any ideas?

[cbrooks118]

I would check the CDI. It controls you spark timing to an extent (working with the stator) You could be getting a spark, however it could be to weak for detonation or sparking at the inappropiate time. I would take one off another bike that runs perfectly just to check for free. If that turns out to be the culprit, buy one off ebay, no need to go with an expensive aftermaket one with the mods you listed.

If that aint it, I would say fuel is the next place i would start.

[burcham400#39]

when it is turning over , is it real fast or at normal speed

[HyBrid00benji]

yeah will have to rob a cdi from somebody. I guess thats all thats left to be wrong with it.! Its sparking good though. But the plugg does smell like gas when it comes out of it. idk..


Its turning over normal, thats why i figured it was making compression.

[QIKLTR]

i would bet its time for a rebuild, ususally when its hard to start its due to lack of compression.

[HyBrid00benji]

it might be due up for a rebuild. You'd think it would try to hit a little though, this thing wont hit a lick. We're goin through it right now checking all the wiring. Still don't know..

[bdtoady22]

did you check valve lash?

[HyBrid00benji]

oh dang, i sure didn't! What is the lash on that suppose to be?

[HyBrid00benji]

I don't think the lash would be something to up and change like that though

[bdtoady22]

i agree that it normally doesnt change quickly unless you mushroom a valve then it close right now just something to check for you go rebuilding it. dont know the lash specs but a dealer would right now just check and see if they are closed up against the cam

[HyBrid00benji]

The CDI box wasn''t the problem/...

[Glenyzracer25]

.0039-.0059in on the intake, .0069-.0089in on the exhaust side.