'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.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • 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???

Related Content


Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017

Should I buy this bike? help....... by Numsa Hul

Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.