backfiring, lean or rich, fuel mixture

[torey3]

Here is a question that we all seem to have with governer/rev limiter removal and backfiring. It seems inevitable that these backfires are occuring when the engines are running at higher rpm's and then the throttle is stopped, then restarted . For some the throttlle linkage/butterfly not closing all the way is the issue, for others not. As a rule of thumb do you all think that when upping the speed on a stock cart by removing the rev limiter or governer we should be adjusting the carb to run a little leaner to counteract the increase in gas at higher rpm's or maybe I have this backwords, should we lean them out a tad? If so, what direction do we turn the mixture screw to make it more lean and which way to make it more rich? Maybe I am off on this, but my cart sure pops and smells gassy.

[lockman1]

To be totally honest with you... I didn't have to adjust the mixture at all on my cart!
But then again, I bought it new, so I knew nobody else did either! (except the factory)

and again... to be totally honest...
I think there may be issues with your cart, other then the fuel mixture!
eg: over reving with the rev limiter not disabled, butterfly on the carb not closing, ect....

I think you really need to go back to the begining, and readjust everything to factory specs,
Get it running the way it should, THEN... do your speed modifications, little by little!

my .02

[torey3]

Lockman,
The rev limiter is not hooked up, the governer is adjusted but not extreme and when looking in the carb, the butterfly is closing completely. I am getting backfires now even when going 1/2 throttle, coasting and restarting. The backfires were worse before and real bad when the rev limiter was connected. I am wondering also if the previous overtightening of the throttle linkage caused the butterfly return spring at the carb to stretch. I would like to get a replacement for that just to see. All of that being said, I still think it is running rich, quite gassy smelling.
08 precedent with 60 hours

[lockman1]

huh... not a whole lot different then the way I'm set up...
I just don't have the backfire and gas smell! (well my cart doesn't anyway... LOL!)

If you feel you should adjust the mixture, then do it!
lightly seat the mixture screw, and turn it back out 1 to 1 & 1/2 turns.

If I remember correctly, turning it OUT more, is consitered "lean"
and turning it IN more is consitered "rich"

I could have that backwards... It's been a really long time since I've had to adjust carbs!

Hopefully someone will chime in and either correct me or confirm it!

[FIXEROFCARTS]

Guys, that screw on the carb is not for fuel mixture, it is for the low speed circuit of the carb.

Try this test:

Screw it in all the way and then just step on the gas a little bit to get the carb to open....it wont start. Then floor the gas, it will then run.

Then make the proper adjustment of the screw 1 1/2 turns from the lightly seated position, then do the same thing, it will start right up.

Lean or rich is controller by the jet

[lockman1]

I stand corrected!

Thanks!

[lockman1]

It took "over night" to think about it...

With the Quadrajet and Holley carbs I used to work on,
adjusting the fuel mixture screws were just for the Idle! (I knew that... I just forgot it!)

I "think" that's why I said: "If you feel you have to adjust..."

again... I still think there's another issue that makes it backfire!

FIXER??? any idea's to help torey3???

[crash12888]

I keep thinking about this (even back to your other posts) and would like you to try something.
Go into the black plastic box under the seat and unplug one of the wires on the lower microswitch.
That is the "kill" micro for the coil/spark plug,
The Idea, I'm thinking when unplugged is when you are off the pedal you will still have spark and will burn the fuel being drawn into the cylinder.
If the backfire goes away it tells me you are getting fuel into the cylinder when coasting from off the pedal and the carb is still not closing all the way or maybe a weak spring that lets the engine vacume pull the throttle open some.

Just throwing it out there.

[torey3]

Here is one other thing that I would like you all to take a look at. The throttle cable doesn't look right to me. As you see in this picutre, the black rubber sleeve is not spread out over the whole throttle cable. When I have streched it over the whole cable, it was the same as tightening the linkage and was preventing the butterfly from closing all of the way. Is the sleeve supposed to cover the whole cable? You guys are great for your help and I do appreciate it.

[crash12888]

It doesn't cover the whole inner cable, it is just an accordian seal to keep dust/dirt from entering the outer cable.
At WOT it should be @1/4 inch from being fully compressed.