backfire flame

bte

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#1
I'm new to 4-strokes, I have a 01 te400 (Husq.) this afternoon I put on a new exhaust and headpipe. After I was done I took it for a spin, after it got warmed up, it would backfire like crazy. Then I noticed when it would backfire it would shot out a flame about 6". Is this correct? I would think that the air/fuel ratio was not correct or the jetting was to rich. That is just me, and I'm no pro. So I thought I would ask the collection of minds that call this place home. The jetting is stock and so is everything else. The exhaust doesn't have a sparkarr. which will be the next thing bought. I am running 93 pump gas and the carb is a Dell'Orto.. If anyone has any info please give. Thanks
 
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#2
Generally speaking, backfires after the installation of a new pipe tend to be the result of an overly LEAN mixture, or over-scavenging at low speeds. If the mixture gets lean enough the fuel burning is VERY SLOW and will still be going on when the exhaust valve opens which causes the flames.

It would be worth your while to check with the pipe manufacturer for suggested jetting changes with the new pipe.
 

Russ

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#3
It also wouldn't hurt to check if you have any leaks in the exhaust. Check all of the joints for "puffing."

Also, remember that on the Dell Orto the screw is probably a bleed screw so when you turn it IN you LEAN the mixture and OUT RICHENS the mixture. This is opposite of most 2-stroke carbs. You may want to try a richer pilot...I have a few laying around. Let me know what you have now.
 
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