09 YZ450F Off Idle issue

3 replies to this topic
  • SM421

Posted May 22, 2011 - 02:35 PM


I'm sure this question has been asked but I couldn't find anything on TT that specifically talks about a jerky throttle response off idle and at slow speeds for the '09.

Normally I use the bike for the track where I have NO issues. But I just came back from 3 days at Durhamtown where I rode a lot of single track. In that environment, I noticed that it was very difficult to maintain a flow at slow speeds because the slightest change in throttle possition caused the bike to jerk forward (like it over reacts to small throttle openings). I also noticed that its very difficult to maintain a steady speed with small throttle openings.

I've had several other brands of 450's prior to 2009 and never experienced this problem.

Anyone have a fix?

  • grayracer513

Posted May 22, 2011 - 02:49 PM


Check your pilot circuit (idle mixture) adjustment. If you have it richer than necessary to get better throttle response, what you need to do instead is switch to a needle with a smaller upper diameter.

This may also be the case if richening the idle improves the matter.

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  • SM421

Posted May 24, 2011 - 12:14 PM


I'm already running a 48 pilot and the fuel screw is at 2 1/2 to 2 3/4. I'll try the NFPR needle and see if that makes a difference. I do recall a similar behavior at small throttle openings with the stock jetting when I first got the bike. The 48 pilot did help some but didn't cure the problem.

I've also got the GYTR 9.6 oz flywheel on order. Maybe that will help as well.

  • grayracer513

Posted May 24, 2011 - 03:42 PM


I'm already running a 48 pilot and the fuel screw is at 2 1/2 to 2 3/4.

Your problem may be that the bike is too rich at idle to transition to the main circuit correctly. Read this and see if it indicates that your pilot setting is correct:


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