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08 450 MXR backfire and popping on new machine???
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Posted by: snowman48

PLEASE HELP!!!! i just picked up a new 08 outlaw 450 and it seems to backfire and pop when i let off the throttle. It only does it when i let off after really giving it. I checked plug was white, which i know is lean, so i turn the air fuel screw out one turn and it turned light brown. It ran alittle better, but still backfireing??? If anyone knows what factory specs are for the carb please let me know. Thanks. I was also wondering if the ziptie mod that guys do on the YFZ450 will work on this quad. There the same carb...Right??? I have a jet kit on the way so i hope that works. Sorry for rambling, i can figure stuff out better if i run ideas by some other people. Thanks again.

Posted by: sleddog66

First off, this is very common on the KTM's. 2 things cause it. The head pipe leaks at the first connection, and also fuel mixture a bit lean. You can read 100's of posts all over the internet on this. If you richen it up a bit, it will cool the pipe and help a bit. Really to cure this you need to seal the head pipe, which is very difficult unless you weld it. Really I would not get too worried about it. Jet the machine properly, and ride it. It wil crackle a little, but not hurt anything. Ever go to a nascar race and listen?

Posted by: snowman48

thank you!!! You just made my headache go away!!

Posted by: GE4x4

I would allmost bet it the header pipe. I took mine off in no time and put high temp sealer on it. It hasn't backfired since.

Posted by: snowman48

i'll put some high temp sealent tonight and c if that works.

Posted by: snowman48

one more thought on this issue. i sealed the head pipe and it seemed to get better, now i'm trying the jetting. it ok but seems to get worse when it gets really hot or lugging it then get on the gas fast then let off suddenly?? It's just this machine is a whole new animal to me from my predator!!