'06 YZ450f hot kicks very hard

7 replies to this topic
  • FriscoKLR

Posted May 12, 2009 - 09:19 AM


I have an '06 YZ450f with about 70 hours since last rebuild. Over the last couple rides its getting really tough to near impossible to kick over (feels almost like the pre-decompression YZ 4oo's & 426's) but only after its warmed up. Cold it kicks over fine. I'm getting ready to check the valves and new timing chain. Anything else to look for that would cause this?


  • grayracer513

Posted May 12, 2009 - 10:18 AM


Possibly cam timing.

  • FriscoKLR

Posted May 12, 2009 - 09:07 PM


Grey, is there anything to look for on the exhaust cam to see if the part that initiates the decompression is working?

  • FriscoKLR

Posted May 12, 2009 - 09:16 PM


Never mind, that wouldn't be temp specific.

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  • grayracer513

Posted May 13, 2009 - 06:17 AM


Grey, is there anything to look for on the exhaust cam to see if the part that initiates the decompression is working?

Yes. You can operate the mechanism manually, and at TDC, you should be able to see the extended decompression pin just behind the cam over the left exhaust lifter, and watch it retract as you move the weight against the spring.

None of the seems related to temperature, nor does cam timing, really, but you should check it. One thing that would be is tight valves. Because of the aluminum head, the valves have less clearance when cold than when hot, and if they're too tight, compression is reduced on cold starts.

  • FriscoKLR

Posted May 15, 2009 - 05:06 PM


It's nothing in the top end. Something mechanical in the kick start is binding up. Gonna pull the clutch basket tomorrow. Any other ideas to look for in bottom end?

  • FriscoKLR

Posted May 16, 2009 - 10:43 AM


Nothing wrong with the kick start mechanism or on the clutch. This thing is really pissing me off.

  • Aka.Goose

Posted July 18, 2009 - 05:26 PM


What did it turn out to be???

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