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To Rejet or not to Rejet

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I recently purchased a 2004 KTM 450 EXC and have taken it on a couple rides.

 

 

When going down hill it backwraps pretty hard (pops). I have tried messing with the fuel/air screw in several positions and it continues to pop when decelerating.

 

 

I do ride in the mountains and change elevations quite a bit.

 

 

 

Will rejetting solve this problem or am I doing something wrong?

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I have the same problem, I have re packed and put a new crush washer in with no change, tried making it richer with no change. Adjusted fuel screw with no change in popping, so I left it and try not to coast much, when I get around to it I'm going to put a new slide seal in, I have heard of it fixing this problem before we will see one of these days.

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Note that even properly jetted engines will backfire/pop on occasion.  I have had good luck in eliminating or at least greatly reducing the popping by  sealing the header pipe exhaust manifold junction with Hi Temp Silicone Seal.  The header pipe most be pulled away from the exhaust manifold first so that the Si Seal can be slathered on the (cleaned) exhaust tubes and then reinserted.  Let cure for at least 24 hrs.

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