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2004 yz450f backfiring/popping

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i just purchased an 04 yz450f and the bike seems to backfire and pop a lot. it usually does it on deceleration. i am from michigan and dont know if anyone has ever tried the jd kit and would like some info on it. thanks.

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My '04 was doing the same thing, so I put a 45 pilot jet in and a little fine tuning with the fuel screw helps matters alot! :thumbsup: BTW I live in Columbus Ohio at about 300' asl.

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what comes stock in them a 42 pilot. did you have to take the carb apart to do that? please help man my bike sounds like an orchestra going off in the background i cant even ride good bc im thinking of it so much.

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The 42 comes stock, and the 45 is the next step up. The jet costs around $5. You need to remove the float bowl to get to the jet. You may be able to loosen the clamps and rotate the carb in place. Just check the schematics in the manual to help locate the jet. Overall it is an easy fix, and you will need to re-adjust the fuel screw for the healthiest idle when done, and then enjoy some pop-free throttle time! :thumbsup: If you are going to a parts shop to get the jet, you should bring your old one with you to make sure you get the right model.

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you can turn the fuel screw out to compensate for the popping. If it takes more than 2-1/2 to 3 turns to get it to stop then go up one on the pilot jet.

The ideal spot for the pilot screw is ~1 - 5/8 turns out from bottom.

here's a great way to tweak it in. scan down to Rick_Kliene's post.

http://www.thumpertalk.com/forum/showflat.php/Cat/0/Number/1355833/page/1/view/collapsed/sb/5/o/all/fpart/1

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Try turning out the fuel screw as suggested first, then a bigger pilot jet. The float bowl drain bolt is all that needs removing. The pilot jet can be accessed thru the opening just in front of the main jet.

James

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I'm having the same problem with popping and backfiring on decel. I have an '04 WR450F Canadian model and live in Colorado where I typically ride between 7500 to 10000 ft elevation in the woods. I have the ZIP TY fuel screw and adjusting it doesn't seem to help. I'm hesitant to go to a larger pilot because I ride at high elevations. I believe the Canadian versions come with a 45 already. I checked when I got it but forgot what's in there. Is the solution always to richen up the pilot? By the way the bike is brand new and has only 60 miles of break in time on it. I'm running the stock exhaust uncorked with the GYT insert. No snorkel and I've clipped the gray wire.

Thanks in advance.

Adam in CO

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The needle clip position can also be set richer, but that would be opposite the usual plan for higher altitude riding.

The next step is to use a needle with a smaller straight diameter and keep a leaner needle clip position. The straight diameter is more effective on deceleration at closed throttle than at steady idle.

The jetting kits use this method to adjust and have 2 needles to expand the range of choices (see banner ad above). At the Colorado 500 last month, I set up the carburetion on a WR450 before the event. Using the high altitude needle (Red marked #4 position), the bike ran great all week at altitudes up to 12,000 ft. A larger pilot jet was not required.

Note that if you have an exhaust leak at the cylinder, jetting will not solve the popping and backfiring. More than a few KTM 525's have had this problem when new.

James

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Hey I just joined and am having this problem too. I have a 45 pilot, a DRM needle, and a 172 main w/a curtis sparks supercharger air intake. I'm on the 4th clip on the neddle...any suggestions?

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