Problem With Starting 07 450

3 replies to this topic
  • jpancelli

Posted April 12, 2010 - 07:55 AM


I just recentley got an 07 yz450f for 3200, here is some background on it;
It was professionaly maintianined by a head mechanic at a yamaha dealer, it only has about 30 hours on it. I have heard people talk about sucking sand into the breahter hose and I'm worried considering I was riding in sandy areas this weekend.
The problem began when I was riding yesterday, The bike was running regularly, I shut it off and let it cool for a little, then went to start it again and nothing happened. It backfires and smoke comes out of the exhaust when I kick it 10+ times. Does anyone have any suggestions as to where to start with diagnostics? PS when I went to bumb start it every component in the engine was running smoothly, sounded like no spark or potentially a fouled plug? dont know much about that aspect of 450s. Any help is greatly appreciated.

  • emrich-55

Posted April 12, 2010 - 06:57 PM


I just had the same problem with my 09 450, i went to start it after i stalled it and it woulnt start. Turned out that my timing chain jumped a couple links. I would check your valve clearance. Do the simple things first like check spark and make sure your getting fuel and if your getting those 2 things than its valve clerance.

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  • jpancelli

Posted April 13, 2010 - 05:26 AM


Thanks for your input. When the timing chains jump does that mean I have to adjust the tensioner? Is that a complicated procedure? Also will that alter my valve adjustments?
-John Pancelli

  • grayracer513

Posted April 13, 2010 - 10:01 AM


The tensioner is entirely automatic; no adjustment. Valve adjustment does not depend at all on chain tension or timing.

If the timing chain jumps, it is normally due to one of two things:

  • Cam seizure, caused in turn by improper assembly/torque od the cam caps or a lack of lubrication, or
  • Binding/kinking links in the chain itself, which interferes with the operation of the tensioner.

If the chain jumped, replace the chain and the tensioner regardless of the cause.

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