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SM421

09 YZ450F Off Idle issue

4 posts in this topic

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?

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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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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.

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