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250F Backfiring

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Hi guys. My buddy got a problem with his yamaha 250F 07.

When he give it gas and let off, it gets this crazy backfiring.

He has checked the hotstart, and the hotstart is working properly.

The plug is also white. He has tried to give it a little more fuel, but it is still just as white.

Please answer as fast as possible! :)

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I have a 2006 YZ250F and it was doing the exact same thing, had it rejeted and it still did it because the accel pump wasnt working mechanic fixed the accel pump and it runs perfect.

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Popping when you shut the throttle is typically a lean condition in the idle circuit. Try adjusting your fuel screw by making the mixture richer (turn counter clockwise) and/or get a bigger pilot jet to see if it helps. Making the main jet larger won't help since the MJ is not being used when the throttle is shut. It's fine for bikes to pop when you suddenly shut the throttle like on deceleration, but if you have excessive popping, this can be fixed by making the idle circuit richer.

Hi guys. My buddy got a problem with his yamaha 250F 07.

When he give it gas and let off, it gets this crazy backfiring.

He has checked the hotstart, and the hotstart is working properly.

The plug is also white. He has tried to give it a little more fuel, but it is still just as white.

Please answer as fast as possible! :)

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I have a 2006 YZ250F and it was doing the exact same thing, had it rejeted and it still did it because the accel pump wasnt working mechanic fixed the accel pump and it runs perfect.

I don't think the accelerator pump is used when you shut the throttle like in his case...

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thanks for the answers, he has adjusted the fuel so the sparkplug is brown now, but he took of the exhaust, and when he looked into the exhaust valves they were all white, is this normal?

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This is my bike we are talking about. The spark plug is still white, the bike is still popping and the red hot pipe is still a red hot pipe :thumbsup: Dont understand what could be wrong. I tried the fuel screw with no help.

IMG_3158.jpg

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Did this just happened or has it always popped? Could a leak just have happened in the carb's boots or has the weather gotten colder? Try the next larger pilot jet.

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I have used it when it was backfiring and the pipe got hot, but i did not know about the white spark plug so i dont know it if has been like this before (New spark plug today). What do you think about the valves?

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The bike shop found the solution of the problem. All the jets in the carburettor was full of shit. The bike shop staked and blow all my jets clean. The bike is now running great! No backfiring and no redhot pipe :thumbsup: Had to pay 190 US $ but is was worth the money.

Hope this can help other people. The mechanic said that it is smart to clean the carburettor and jets 2-3 times every season.

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