Well i've adjusted the mixture screw at the bottom of the carburator but it didn't help.

I still have back-firing in the exhaust pipe when i brake on my engine.

Can anyone help me?

If your out 2.75 to 3.0 turns on the fuel screw, you may want to consider the next higher pilot jet. Some popping is ok.



99 WR400f, YZ timed, MX-Tech suspension, Scotts steering damper, White Bros E-Series (12 discs), tapered header and a/f. Kouba T-handle for the fuel screw. Works Connection billet throttle tube and frame guards. Cycra Pro-Bend, triple clamp mount handguards. Thumper Racing rad guards, Renthal Jimmy Button highs, YZ Tank and IMS seat, YZ number plate, odo removed, EKP, 48PJ, 175MJ at 500-1000' Thanks James Dean!

My friend had a backfire that we could not get rid of by jetting. He took off his pipe, gaskets, cleaned surfaces and reinstalled it. The backfire went away and we assumed it was an exhaust leak. Might check that out.

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