Flames come out the back!!!!

So i just bought my bike (03 yz 450f) Sweet machine, damn fast. I was riding around dawn and my buddies said i have huge flames coming out the back. I think its mainly when i let off the gas because it back fires sometimes (sounds cool though) not huge backfires, seems normal to me.

Is this bad?

what could it be?

thanx

kevan

i would presume that to be normal... small backfiring on decel is pretty normal, and usually when you have backfire some flame shoots out the exhaust , most of the time its not noticeable but if it wasn't very light out you might see it. also, it might be running a tad lean try messing with the fuel screw.

Yep what he said. Didnt you notice that the header pipe gets RED HOT too? ALL normal and yes you sound a little lean.

Exhaust decel backfire is almost unavoidable, and unless it gets to the point that there's a risk of blowing your muffler apart or starting a fire, it's harmless. But you can at least nearly get rid of it in most cases.

It's usually caused either by lean idle mixture, or an air leak in the exhaust system.

If you don't have one now, get an extended idle fuel screw. FCR carbs are sensitive to changes in altitude and temperature, and need to be tweaked from time to time. The extended screw makes it easier (possible) to do.

Air leaks in the exhaust normally happen at the midpipe/header joint, but it can be anywhere else there's a joint in the system. Rule this out as well as you can before playing with your idle mix, because otherwise, you may end up running too rich a mixture in order to cover for the air leak.

So i just bought my bike (03 yz 450f) Sweet machine, damn fast. I was riding around dawn and my buddies said i have huge flames coming out the back. I think its mainly when i let off the gas because it back fires sometimes (sounds cool though) not huge backfires, seems normal to me.

Is this bad?

what could it be?

thanx

kevan

time for a spark arrestor?

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