06 kx250f backfiring problem

ever since i got the bike its backfired bad, and it wont idle when started but when the motor warms up it idles too high, the needle clip is in the right spot, the fuel screw is turned out 1 3/4, stock jetting, and ive made sure the timing marks lined up,stock pipe and theres no exhaust leak, still cant figure it out and have run out of options...any help?i can post a video if needed

Buy a BRAND new #42 pilot.

Make sure packing is fresh

Adjust fuel screw for a perfect hot idle.

If the bike is reving up on its own with out any throttle there could possibly an air leak. i would try a leak down test before you try to rejet the bike.

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