backfire when getting off cart

[Dog321]

It doesnt do it all the time....but more times than not....also once in a great while it'll backfire once on letting off gas after a speed run....should i back out the air needle 1/2 more turn ?...would that have anything to do with the shut off backfire?

[Dflowe]

You need to adjust the throttle cable where the carburetor butterfly closes all the way when you let off the gas pedal. I usually adjust it when the carb in my hand and I make sure it closes all the way shut and no light comes through. Also, you want to be sure the idle screw is adjusted to where the throttle linkage never touches it. It's useless anyway, the switch on the gas pedal is going to cut the engine off regardless of the idle adjustment. I suggest the throttle cable have plenty of slack in it too. Many people do just the opposite trying to be sure the butterfly open all the way and they get maximum speed. My experience is that they end up with a cart that backfires.

[SandbaggerYDRA]

Originally Posted by Dog321

It doesnt do it all the time....but more times than not....also once in a great while it'll backfire once on letting off gas after a speed run....should i back out the air needle 1/2 more turn ?...would that have anything to do with the shut off backfire?

It's not an "air needle", it's an idle fuel mixture adjustment. The more you back it out, the richer the mixture gets (at idle). A little richer idle mixture can help smooth over hesitation when transitioning from idle to WOT, but it could lead to more unburned fuel finding its way to the hot muffler which can result in backfire. Your best bet to limit backfire is to make sure the throttle valve is completely closing when you let off of the gas pedel.

[Dog321]

Thanks guys....i had plenty of slop in my throttle cable...my idle adjustment scew was backed out to touch nothing already....this morning i backed out the"fuel mixture adjustment" screw a half more turn....still get the 2 second POW....but increased power on take off....think i know what i have here....i took the clones muffler(which was on top of motor) and turned it down in front of valve cover(see pic)...i think the fumes are collecting in can(muffler)

[SandbaggerYDRA]

Originally Posted by Dog321

Thanks guys....i had plenty of slop in my throttle cable...my idle adjustment scew was backed out to touch nothing already....this morning i backed out the"fuel mixture adjustment" screw a half more turn....still get the 2 second POW....but increased power on take off....think i know what i have here....i took the clones muffler(which was on top of motor) and turned it down in front of valve cover(see pic)...i think the fumes are collecting in can(muffler)

The style of the muffler may also be contributing to the backfire. There may be hot spots in places that just make backfires the rule rather than the exception. Stock cart mufflers are usually very large cans which tend to spread the heat out over a larger area, which may reduce the occurrence of backfires.

When I was a kid and had go-karts and mini-bikes, those little Briggs an Stratton 4 HP engines would always backfire when you let off the throttle after a high speed run (of course we strapped out the governors too). The mufflers were simple 6" long cylindrical chambers that would actually glow dull red after a really hard run. It's not hard to understand how you'd have backfire issues under these conditions.

[Dog321]

I totally understand