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sthedreem

03 YZ450 - Normal or Problem

8 posts in this topic

I have an 03 YZ450 with stock jetting. When I roll on the gas I get something like a stutter/hesitation. If I pin the throttle, no hesistation at all?

I am in Florida, so altitude is not an issue,

The clip is set on the #4 slot on the needle (stock position per Yamaha manual)

Anyone has any input on this?

Thanks

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Is the stutter at less than 1/4 throttle?

If so, adjusting your pilot screw should fix it.

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It is at a range from right below to just above 1/4.

I tried adjusting the needle, and I had the mechanic that has worked on it for me try to adjust the pilot screw, but he could not eliminate it. He told that some YZ450 run like that.

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It is at a range from right below to just above 1/4.

I tried adjusting the needle, and I had the mechanic that has worked on it for me try to adjust the pilot screw, but he could not eliminate it. He told that some YZ450 run like that.

mine did that too until I rejetted it w/ JD Jetting and put a quickshot on it....

I would check the jetting spec for your altitude 0-700ft - as stock jetting may be part of the issue for you in florida as well as check the AP Duration and then I would try the AP wiring mod for instantaneous throttle response

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mine did that too until I rejetted it w/ JD Jetting and put a quickshot on it....

I would check the jetting spec for your altitude 0-700ft - as stock jetting may be part of the issue for you in florida as well as check the AP Duration and then I would try the AP wiring mod for instantaneous throttle response

I'm new to 450's. What is the AP duration and AP wiring mod? I like the sound of instant thottle response.

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I second the J/D jetting kit. It definately improves throttle respose. Also, varying temperatures/humidity/altitude, all have an effect on the fuel mixture, thus requiring you to readjust the Fuel Screw, for the changed condition.

Ap duration refers to the Accelerator pump...ie. how long the pump's squirt of fuel lasts.

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