Just got My 05' yz450f Keeps backfiring like craazy!!!

I just bought a 05 yz450 off craigslist for 1900 ( i know, suspiciously cheap) the bike looks like its in good condition, it goes threw the gears smoothly and starts first kick. Does anyone know where I could find an owners manual online? The bike has some cheap aftermarket pipe on it and it is backfiring constantly! is this some sort of jetting issue or will it backfire less after its been heated up and ridden a while?

My dad's 05 does the same thing and even shoots flames. After you warm it up it will go away.

I just bought a 05 yz450 off craigslist for 1900 ( i know, suspiciously cheap) the bike looks like its in good condition, it goes threw the gears smoothly and starts first kick. Does anyone know where I could find an owners manual online? The bike has some cheap aftermarket pipe on it and it is backfiring constantly! is this some sort of jetting issue or will it backfire less after its been heated up and ridden a while?
Your backfiring is probably due to a leak in the exhaust. One of the reasons the Common Threads sticky says "Look Here First" is because it has all this stuff in it already:

http://www.thumpertalk.com/forum/showthread.php?p=3710599#post3710599

http://www.thumpertalk.com/forum/showthread.php?p=3350613#post3350613

http://www.yamaha-motor-europe.com/community/service/manuals.jsp

thanks gray you kickass

Backfiring is one of a few things. As mentiond above leaking exhaust, either at the header/midpipe connection or at the cylinder head. Stuck hot start. Stripped hot start screw. Clogged pilot.

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