2007 450 not running right, will only bump start, but runs rough Thanks

[Davey762]

Hey guys,

My bros 2007 yz450f.. with about 35 hours on it doesnt run right. The kick starter is harder to kick over, seems to lock sometimes... and wont start that way. Was able to bump start the bike down a hill, but it was running weird afterwards.

Thought the decomp might not have been working, but pulled the head and its fine. Next i'll probably check the clutch out and see if everythings ok in there as it was just torn apart and swapped out with a full hinson assembly.

I'm not a yami guy, and my bro is new to their 450's.. so I'm wondering if you guys have any ideas? Timing? Valves need adjustment maybe?

Thank, Dave,

[grayracer513]

If the engine is suddenly always harder to kick over than it was, check the cam timing.

[Davey762]

Thanks for the reply, I thought of that.. but wasn't sure how the timing would suddenly get out of wack? Cam chain tensioner stop working and let it skip a tooth?

[JamesNad]

my buddy had a 02 crf250, and the thing has a few hours on it, gets ridden alot, and he blew it up and a local shop rebuilt it and for maybe 10 hours it ran find then he was ridding it and it died, and couldn't get it kick start so bumped it and started but runs alittle rough, and turns out the valve lash was alittle tight,

i would check that just to rule it out, and i understand the honda's are different but could be a possibility

[grayracer513]

Thanks for the reply, I thought of that.. but wasn't sure how the timing would suddenly get out of wack? Cam chain tensioner stop working and let it skip a tooth?

The most common problem is camshaft seizure, which normally is a result of either really poor maintenance or improperly torquing the cams after a valve adjustment. But some late '07's and early '08's had problems with chains kinking and tensioner damage. I'm not sure which order that happens in, but both problems seem to occur at the same time, so I'm guessing one causes the other. Either way, it's worth looking into.

[Davey762]

He checked it out last night and the cam chain was kinked and the exhaust cam was out by two teeth. Weird that the chain kinked after only 35 hours.. but apparently its been a known problem like grayracer says.

Wonder if there is a way to check the cam chain tensioner, or just buy a new one?

[grayracer513]

Weird that the chain kinked after only 35 hours.. ...

Wonder if there is a way to check the cam chain tensioner, or just buy a new one?

I just pulled a friend's '06 apart last night with the same problem. Fairly low hours, bought new in 6/06. First '06 I've seen it in.

Checking the tensioner is easier if you're familiar with the feel of a good one, or if you have one to compare to. Using a small screwdriver, it should wind all the way up smoothly, with no sudden or major changes in spring tension at any point. Hold the plunger in with a finger, and then let it extend slowly. The plunger should extend smoothly and positively as you let it out, not catching or snagging anywhere, and you should not be able to push the plunger in without turning the screw no matter how hard you try.

They're pretty cheap. If you're not sure, just get one.