YZ450 won't run when it heats up

4 replies to this topic
  • atropine

Posted December 23, 2010 - 10:51 AM


06 YZ450, have owned it for a little over 3 years, has run great until recently. I first noticed something amiss about a month ago when partway though a ride it wanted to stall out at idle. Next thing I noticed was a lot of decel popping, so I played around with the fuel screw but couldn't make it go away. Next thing I noticed was a cracked head pipe. Replaced the head pipe, but it still wasn't running right and was blowing white smoke out the crankcase breather tube. Thing figured out it was losing coolant, so tore the top end down. Everything looked OK but the head bolts had loosened way up and was likely allowing coolant to leak into the cylinder and burn off, hence the white smoke. So we replaced the head and base gaskets, replaced the rings since we were there already, and did a valve adjustment. The valves weren't too far out, and the cylinder and piston looked good. When it is cold, it starts up on the first kick now, but as soon as the bike gets warmed up it starts to run like crap. If you keep the throttle opened up above idle it won't die, but as soon as it returns to idle it dies. I have played around with the fuel screw and it doesn't fix the problem. I am about 1.75 turns out on the screw, which is where I think I always was in years past. Any thoughts?

  • tech24

Posted December 23, 2010 - 12:14 PM


I'm not too good with carbs (if thats even where the problem is) but you may want to check float height and float needle condition maybe too much fuel getting in to bowl?????

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  • atropine

Posted December 28, 2010 - 09:07 PM


Well, looks like I just needed to play with the fuel adjustment screw a little better because it seems to be running fine today! I guess the change in the weather and my tweaking with the fuel screw got it out of whack, but all is well now. Not losing any coolant now, and all seems to be well.

  • sneipfmx

Posted December 29, 2010 - 03:53 PM


take off your cam chain and move the cams and se i they are hard to move.i have seen it on some wr 450.have you lost oil pressure any time?

  • atropine

Posted December 30, 2010 - 05:04 PM


It is all fixed now. It was just the pilot jet being partially clogged from sitting and the fuel screw just not adjusted perfectly. Got the pilot jet cleaned out and the fuel screw adjusted and it now runs like a champ; starts up on first kick and no more problems. In the meantime, I got a good deal on a leftover 2010 so I pounced on it. Now the 06 is up for sale! Thx everyone.

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