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XR400 major backfire!!!

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Hey everyone, been lurking around TT for a while, awesome site with a ton of great info!

Anyway, I just bought a cherry '03 XR400 a week ago. It is bone stock for the most part(brush guards, fork guards, etc....). It does have a K&N filter that I put in it and a Baja designs sparky with no baffle. It came out of Las Vegas so I'm sure it's jetted for much lower elevation than I will be riding. Most everything I ride is in Utah and around 4500ft and up to around 8000ft. I noticed when I ride the bike here at home it backfires consistently when I let off the gas and dies shortly after.

I pulled the carb apart to check what jets were in it. Currently has a 142 main and 52 pilot jet. I would think that would be fairly close to where I need to be. The bike starts really easy so I'm assuming the pilot circuit must be fairly close.

I currently have the fuel screw out 2 turns from buried. I adjusted it in and out a few more turns, but this seemed to do nothing.

The needle had a part number on it of a A16A I think. Does this need to be changed maybe to a different needle?

Just trying to figure out a place to start at this point. Any ideas?

Thanks in advance Matt

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With those intake and exhaust mods, the main is too lean. Should be more like a 150-152. The A16A needle is fine. Should be in the middle clip position.

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