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Discussion Starter · #1 ·
I have a 2006 TRX 250 EX which has some issues. The carb, jets, airbox and filter have been cleaned. The carb had very little residue in it when I pulled it apart. The engine will only start with the choke on and will rev up but backfires with the choke off and will die as soon as the revs drop. It seems as if the timing chain has jumped the sprocket. I will check the valve clearance and compression. I need some tech info on replacing the cam chain, pulling the head if necessary. The engine sounds good mechanically and doesn't smoke. The rev happy daughter was stuck in the mud. I don't have a service manual but do need a copy of the pages which apply to disassembly of the top end and cam chain replacement. Is the cam chain continuous, have a master link or is it pinned and pressed? Can it be fed thru the tunnel and around the crank? I've done this several times on older sportbikes. Any comments or help would be appreciated.
 

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Welcome to the forums, I would be reluctant to say your issue is in the carb. it has a rev limiter for those rev happy daughters...lol I don't think your issue is in the timing chain you may need a valve adjustment though . The ID. tag on the frame will tell you the valve gap.
 

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Discussion Starter · #3 ·
250 EX cam timing

Yeah, thanks. What kind of deal is the cam chain tensioner. The older setups could be locked back which would give you slack. However I don't see this on the outside of the head. I figue this may have contributed to the problem.
 

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I don't really know about the 250EX engine design, but the 350 Rancher doesn't have a cam in the top of the head and it uses push rods to move the rockers. The 250EX may be set up the same way. That might explain why you don't see a chain tensioner. Just a thought. Maybe someone else will know about that.
 

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They also don't make an aftermarket cam just higher ratio rocker.Makes sence helmut.
 
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