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Discussion Starter · #1 · (Edited)
Every once and a while I get a nice little pop when it backfires on downshifting. It only happened maybe 5 times or so I'm just wondering what it could be from. The carb hasn't been touched. It has a k&n air filter and stock exhaust, but it seems like the end cap was removed and another put in place and it is open. Did these have a spark arrestor? Maybe the previous owner removed it as the exit hole looks pretty large and in the box of parts he gave me looks like a cap with some thing that should go in the exhaust?

Other than the occasional backfire it rides really nice and I had a bunch of people looking at me like WTF is that he is riding :)
 

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Your bike is probably running a little lean and exhaust is popping a bit. Not a huge deal, but nothing a jet kit won't solve.

BTW, a true backfire is when the bike blows fire out the intake. If you have that happen, then you've got a whole different problem, but I kinda doubt that's the case.
 

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+1 The bike is probably runninga tad lean. The other possibility is an exhaust leak, but that would "pop" more frequently.
 

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Discussion Starter · #4 ·
My buddy said he saw a "flame" out the exhaust on one very quick downshift. I was still going pretty quick and downshifted to second and let the engine help brake the bike. It only happened one time though and then it didn't do it any other time I downshifted.

I kept checking but the fans never came on the entire ride in 80 degree heat.
 

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The flame was just caused by valve overlap. There's a short period of time (fractions of fractions of a second) where the intake valves are opening and the exhaust valves are still closing. Fuel gets sucked up into the exhaust port, it ignites either in the port or the pipe and a bit of flame shoots out. It's not really a bad thing. But like yetimcclin said, as long as it's not going back into the motor. That's why they call it a back fire. That can be bad.
 
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