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04 crf40 backfiring.

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Hey guys. I,m trying to help my friend with his bike. It keeps backfiring on decel, I tried playing with the fuel screw, and moving the needle clip up and down. I kinda know what I'm doing but I don't know how to diagnose carb issues. I just trial and error it until I learn more. I'm pretty sure he has the stock jets, and I made sure the float moved freely when I put the carb back together. Any suggestions?

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Some backfiring is normal. If its excessive then a cracked header or clogged pilot jet can be the issue

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Set your pilot up for idle, (Bike fully warmed up) then leave it alone. Check for any air leaks around the header especially. As has been said, popping under decel is normal, more so with a more open exhaust.

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Thanks guys. I'll check his exhaust. The p.o. did take the spark arrested out. May e get a new one, or reach the muffler? I'm talking big backfires, not little occasional ones.

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I had a 450 with a very open 4:1 system. When it popped, it shot flames out a foot long. The sparky was always clean that way.....:thumbsup:

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