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Bought the JD Jet Kit - did not solve problem HELP JD!

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I posted a few weeks back about my '04 WR450 backfiring on decel with throttle closed problem. As I said then, I ride mainly between 8000 and 10000 ft elevation in Colorado. Per your suggestion, I bought the JD Jetting Kit and installed the red needle in the #4 position. I also took the entire exhaust system off, inspected and reinstalled it. The exhaust is stock except I've changed out the muffler insert to the GYT-R Yamaha insert. I then verified that I do not have an exhaust leak at the head by running the bike and feeling around for exhaust flow around the header. It's a Canadian model, and I'm running a 48 pilot jet already (stock). Rather than go to a 50 you said I should change out the needle.

I checked my map yesterday when I was riding and it was 8800 ft. I can tell no difference between the stock Canadian needle and your red one. I understand that changing the needle clip position will not richen the mixutre when the throttle is closed on decel, but I moved the clip to the 5th position just to try it and all it did was muddy up the 1/8 to 1/4 jetting. There was no difference in the decel backfire.

James I am at a loss, this bike really lets out a loud backfire on decel. This is my third WR and I'm used to the popping on decel just not this loud backfire.

Help! Should I go to a 50 pilot even though I ride at high elevation. Why would this bike need such a rich pilot circuit? :cry:

Thanks so very much for your help.

Adam in Colorado

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The loud backire may not be a jetting issue now if you are on the edge of running rich. Your comment about clip #5 being too rich confirms that a richer setting isn't an option (on this needle).

Try a #50 pilot jet and see if it still backfires loudly on deceleration. Another option is to switch to the blue marked needle in the 3rd from top clip position, which will also be richer at 0-1/4 throttle only.

What you might also try is to decelerate with the choke on to see if excessive richening will be adequate. If it still pops badly with the blue needle, there may still be a small, undetected exhaust leak.


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