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backfire on decel

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yz250f, I am assuming it is running too lean. Assuming I should slowly back out the fuel screw to richen mixture first, and then if necessary adjust pilot? TIA.

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No. Fuel screw should be set for a perfect idle.

First check for exhaust leaks. Try fresh muffler packing.

After the above you still have a issue, you need to learn to ride harder. You have a race bike. Hard on the throttle, hard on the brakes. No coasting. Coating is for woods and trail bikes

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If the bike runs well, then I would leave it. Mine was backfiring like a SOB and had an off idle studder after I installed a new muffler and the JD kit. Turns out it was too lean. I made the pilot richer a few turns and ended up at 3 something, so I bumped up the pilot to a 45 and I was golden at about 2-1/4 to 2-1/2 turns out. It still popped a little after being hard on the gas and then coasting like if I was on a road or something, but like William said, it's normal.

The biggest thing is that it idles well, and more importantly for me, it hot starts well! When I'm riding and I stop for a break, or to talk to someone, I like to turn the bike off and it irritates me if she doesn't fire up after the second kick! (with HS lever).

You can warm your bike up and richen the pilot with the fuel screw a eighth or quarter of a turn, then ride it a little bit and see how it rolls off idle (we ain't talking about the AP, so no need to crack the throttle) how it sounds when coasting from low to medium throttle and most importantly how the idle runs. Then shut it off, pull the hot start lever and see how she starts. If it takes more than one or two kicks, then you need to lean the mixture a little and just deal with the popcorn machine :thumbsup:

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