2001 450 es backfiring

Sounds like it is running rich, mine did that when I had the wrong jet in it, I put in a smaller jet in and now its ok. Have you played with the jet, needle setting, or A/F mix recently? What if any mods do you have? does it backfire only after a high speed run or at any time? A list of mods and jet, A/F screw and needle setting etc will help alot.

The backfiring starts after you ride a few minutes, then when you accelerate and let off of throttle it backfires and sometimes under downshift it backfires, have not adjusted fuel mixture, I do not know much about adjusting carb. I bought the Atv used a few months ago , not sure if it has stock jets or not, do you have part #'s by chance for factory jets and needle. My atv is stock except for 27" Vampires and a highlifter lift kit.

Thanks for your help..

the stock jet for the foreman 450 is a oem#130, I am not for sure on the needle. from the factory the air/fuel mixture screw should be around 2.5 turns out and the e-clip is usually set in the middle notch of the needle.