Hard to Start 2006 YZ450

4 replies to this topic
  • gabrams

Posted August 02, 2009 - 10:31 AM


I was wondering what people thought of this problem. i didn't see anything in other threads. I just did a clutch and pulled my clutch basket out and check it and put it back in (may be totally unrelated, just throwing out the information). Clutch seems to be fine. The last time, and this time when i went out to the track my bike has been very hard to start hot. It started right up cold with no issues i noted, but when hot it is a beast and doesn't feel/sound right. Sometimes it is hard to kick, or get the kick started, like just there is too much compression and i pull the hot start (which i never used to have to use) and it seems to help get it moving. It almost feels locked up sometimes. it doesn't seem like it wants to fire or the compression sounded weird when i kicked it over. Sometimes it just feels like a hollow kick. Once it's started it runs fine. If i come in from laps and turn it off and try to restart immediately it displays these symptoms. I was thinking valves out of spec (haven't been checked in 8 months), jetting (not sure if it would display these symptoms), something i did when i pulled the clutch basket (if i didn't mesh the gears right but i don't know if it would/should have any effect when it's in neutral), timing chain (don't know the symptoms), or is it as simple as a plug (doubt it but just came back from track and not going to look at it for a day). Any thoughts would be greatly appreciated.

Update: could water in the gas have caused this? i just drained my bowl on my carburetor and the problem seem to have gotten better. a lot of fluid came out of the bowl but I'm not sure how much should be in there. It seems to have fixed the resistance to kick issue and seems to be starting better hot, granted i just did a garage test and my failure earlier today was after riding laps. Another note is that my last two track days have been rain/wet days and I'm wondering if water worked its way into my gas somehow. I'm not sure if it's fixed but i'll at least do another track day before ripping apart. I would still like some advise. Thanks.

  • usmcpaul

Posted August 02, 2009 - 05:48 PM


I had water in my gas a few weeks ago and my starting problems surfaced when it was cold, not hot.

I got it started (after a visit from the Ether Bunny) and it ran fine, however when it was cold, it would not start, or the needle would stick. I had it stick open and shut on 2 different occasions. So I drained it completely and it fixed the problem.

I had no 'feel of lost compression' either, not saying it can't happen, but it didn't happen to me.

Checking the valves is a quick process, so why not start there?

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  • grayracer513

Posted August 02, 2009 - 06:22 PM


Easy starting cold together with hard starting hot is a sign of being overall too rich. If you did jetting work during the winter, this could be the whole problem.

Also, check the cam timing.

  • gabrams

Posted August 30, 2009 - 04:37 AM


Just to close out the thread, after playing with the jetting with no progress i decided to dive into the engine, which the required the help of my mechanic at Total Control Racing Suspension in Burlington NC. What they found was that the cam chain tensioner had failed and my cam chain was also extremely stretched. So obviously those two parts were replaced with OEM parts. After almost a full engine tear down to ensure that there was no other damage, and checking the valves (which always seem to be in spec), and reassembly the engine runs great.

  • Aka.Goose

Posted September 01, 2009 - 07:11 AM


Damn cam chain tensioner!
That one got me too...There must be a really crappy Chinese spring that was actually made for a child's toy inside there, or something...Maybe once it goes through a few extreme heat cycles it looses it's tension?

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