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backfire on deceleration

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just put new wiseco std piston in my 06 and now on decel it backfires. Any ideas what this is?

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Is it like a loud pop or pop-POP when using the high revs and compression to decel?

It's been almost 5 months since I've riden but I'm pretty sure that my 07 does that stock. I just assumed it was the big bore + hig compression + straight pipe exhaust...

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its fine.. your running lean with the throttle closed but it doesnt matter

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I have 2 450's, neither pop on deceleration, if there popping I'd look for a leak on the exhaust pipe or richen the fuel screw a touch. Properly set up they don't pop

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thanks for the info, I will go out on fuel screw. Anyone suggest going up to a 45 on the pilot I have stock 42?

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I would suggest you put that piston in properly first.

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I have 2 450's, neither pop on deceleration, if there popping I'd look for a leak on the exhaust pipe or richen the fuel screw a touch. Properly set up they don't pop

Mine has just been rebuilt, where would and how much would i adjust the "fuel screw" to make it a little richer? Isnt lean bikes put huge stress on the motor?

thanks

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I have 2 450's, neither pop on deceleration, if there popping I'd look for a leak on the exhaust pipe or richen the fuel screw a touch. Properly set up they don't pop

I second the exhaust leak

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Mine has just been rebuilt, where would and how much would i adjust the "fuel screw" to make it a little richer? Isnt lean bikes put huge stress on the motor?

thanks

http://www.motocrossactionmag.com/me2/dirmod.asp?sid=&nm=&type=news&mod=News&mid=9A02E3B96F2A415ABC72CB5F516B4C10&tier=3&nid=6E5BCFD99FD242B28032722A4D5D52E3

Turning the fuel screw out lets more fuel into the engine and creates a richer mixture. It's recessed on the bottom of the carb. I use a detachable screw driver tip to turn it or you can get a more permanent fuel screw with a knob on the end.

Indeed. Go out on the screw for a lean pop on decel.

Also, how cold was it out? I always remember, COLD=OUT. If it's cold out and your popping turn the fuel screw out. I usually only get the popping when it's pretty cold out (below 45 at least).

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