Hard to start YZ450F

2 replies to this topic
  • Methotic

Posted December 02, 2012 - 09:39 PM


Well, by the title you are probably thinking I meant it won't start, But I really mean that I can barley turn it over! I have a 2006 YZ450F and I am believe these bikes are equipped with an auto compression release on the exhaust cam. I've seen videos online of people starting the 450s, just gently kicking it over. I could start my KX250F with little effort. For some reason this Yamaha really requires a hard stomp on the kicker, and I mean with all of my weight! Any suggestions?

Edited by Methotic, December 02, 2012 - 09:40 PM.

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  • grayracer513

Posted December 03, 2012 - 07:09 AM


Check your cam timing. The auto decompression system is built into the exhaust camshaft, and the timing of it is important to its function. If the exhaust cam slips a tooth or two, the setup won't work right.

If you find it has slipped time, the chain is probably "kinking" (tight, binding links). Plan on replacing the timing chain and the tensioner.

  • Methotic

Posted December 03, 2012 - 02:08 PM


Well I popped off the rocker cover and there was no surprises leading to the exhaust cam. But here is what I found: I lined up the TDC marks on the stator and the exhaust cam lines up perfect. One dot to the left and one directly up at a 90 degree angle. The decompression system functions, it recoils towards the inner part of the cam. The intake cam is slightly off by what appears to be one tooth. It is a tad to the right.
Posted Image
Posted Image

Edited by Methotic, December 03, 2012 - 02:17 PM.

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