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4esh_numa

What Causes my WR450f to Backfire?

4 posts in this topic

Open exhaust - Not stock muffler

Air leak in exhaust

Inoperable ACV

Excessively lean jetting

These are typically the main reasons

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Open pipe is the number one reason., Stock bike has decel pops but the muffler, well, muffles it. Also, when a lot of guys change a header, they reuse the gasket in the head. Sometimes you can, sometimes you cannot. Also a hard fall can jam the pipe against the gasket, malforming it and also creating a leak. Lastly, if everything checks out and all you have are some pops and not explosions, let it go. Do not try to jet it away unless you want to slow the bike down.

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