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Hello all,

I currently live in Phoenix Arizona and I am having problems with my 2006 KX450F backfire. Its rides perfectly fine and has all the power in the world, does not lack on the responsive side at all. But whenever I engine break I pop A LOT. "Poppopopopopopopopopop" and its whenever I am slowing down after either going fast or slow. I want to know how to stop that, I understand that some popping is okay, but its a lot, spits fire sometimes after going fast.

I am not sure what current jets I have in the bike, because the previous owner did not know, but I am thinking of going to a 180 main jet, 42 pilot, 55 leak jet (from 70 stock), throttle clip position 4th from the top, and 2 turns out on the fuel screw. I have heard a lot of people changing the leak jet from 70 to 55 helps a lot overall. I am not sure on what to use for the elevation wise on the jets.

I have tried to lean and richen the fuel screw before but nothing has happened.

Any suggestions of what I should do? Just thinking of getting JD Jetting kit and going from there.


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Deceleration popping can be a bad pilot circuit, which includes the fuel screw, a bad header sealing washer, or a cracked header or leaking hot start. A bad hot start plunger or cap is extremely common . Decel popping is essentially a lean condition or air leak symptom .

You need a  BRAND NEW 45 pilot, a fresh oring on the fuel screw, and properly adjust the fuel screw.  42 is too small unless you are above 8500ft.

No other part of the carb causes decel popping.  Decel popping is normal if you down shift to high rpms, to some extent.

You have to tune the fuel screw starting at 1 turn out and a LOW IDLE. As low as it will go on a hot motor. Then turn the fuel screw out to raise the idle. It is subtle. Adjust the idle screw as needed after.


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