Backfire!

[Texas001]

What can cause a cart to backfire. I can be driving along, left off the gas to slow and then step back on the gas again and BANG. Replaced the spark plugs, new carburetor, fuel pump is working fine, maybe air leak? I have no idea so I need help. Also, can make it backfire just by revving up the engine going on and off the gas. Off and then on and backfire. I know you guys have some clues, I have none. Oh, I adjusted the carb so that the when off the gas pedal the linkage is completely closed. Spinning it over with just enough pressure on the gas pedal to do so, the engine doesn't try to start. I suspect that maybe the linkage is not letting the carb close all the way but what do I know? Thanks to those who read and to those who help.

[Texas001]

Disregard my original post and here is some things I did and now read this.


Just replaced the carburetor and now she backfires. Made sure that the idle screw is all the way out and so the butterfly should, I say should, be able to close completely. The linkage at the carburetor has a bit of slack, so it seems. You think that what I have is a crappy chinese carburetor or something else? I spent 1 1/2 replacing the carburetor and now backfire. I also noticed that it feels like it is surging was I drive slowly? Can someone sum it all up for me and if the answer is chinese crappy carburetor I will accept that. I am headed for my shop and going to open up the old carburetor and check needle and seat and float etc. I might just clean up the old carb and reinstall it and see what happens. Comments?

[trig123]

Originally Posted by Texas001

Disregard my original post and here is some things I did and now read this.


Just replaced the carburetor and now she backfires. Made sure that the idle screw is all the way out and so the butterfly should, I say should, be able to close completely. The linkage at the carburetor has a bit of slack, so it seems. You think that what I have is a crappy chinese carburetor or something else? I spent 1 1/2 replacing the carburetor and now backfire. I also noticed that it feels like it is surging was I drive slowly? Can someone sum it all up for me and if the answer is chinese crappy carburetor I will accept that. I am headed for my shop and going to open up the old carburetor and check needle and seat and float etc. I might just clean up the old carb and reinstall it and see what happens. Comments?

Why did you replace the carburetor to begin with ?
If the one you removed first is the OEM then yes by all means see if you can repair it.
I would toss the China one but some people make them work. I just never any luck with them VS the OEM.

[Cartmaster]

before doing anything else. With the ignition turned off, place an ear close to the middle of the floor and slowly push the gas pedal until you hear a faint click. This is the pedal micro switch operating. Once you have identified this sound. do the same again but look at the carb operating arm for the throttle. If the carb butterfly starts to, or is already open before you hear the click from the pedal switch. That will be your problem. You must set up the operating cables for the carb so that the switch clicks before the carb starts to open.

My reasoning here is both the backfiring and surging while trying to drive slowly.

If the carb is slightly open when the micro switch is operating, then gas is already entering the combustion chamber before the spark plugs fire causing both symptoms you describe.

I also second the thought that the OEM carb should be serviced and used over the option of a chinese carb.

I assume you are checking that the current carb is actualy closing fully as you seem a bit vague with your "should be" comment LOL.

[StoveBolt]

I had a surging problem once. it was an adjustment on the linkage that runs in front of the timing cover. It has a little piece of cable in the middle of it and has to have a little slack in in (droop a little).

[Cartmaster]

Op has stated that there is slack at the carb linkage but not sure if he means the link directly at the cab or the rod link you mention. I am sure we will figure this out quickly. It seems that the issue started when he replaced the carb, and as Trig asks, why did he change the carb? Sometimes when changing carbs it alters the geometry of the linkages to the butterfly and it opens sooner when you push the pedal. I have also seen the butterfly return spring to be too weak on the clone carbs and it could be just that not closing the butterfly completely when letting off the gas.

[StoveBolt]

Originally Posted by Cartmaster

Op has stated that there is slack at the carb linkage but not sure if he means the link directly at the cab or the rod link you mention. I am sure we will figure this out quickly. It seems that the issue started when he replaced the carb, and as Trig asks, why did he change the carb? Sometimes when changing carbs it alters the geometry of the linkages to the butterfly and it opens sooner when you push the pedal. I have also seen the butterfly return spring to be too weak on the clone carbs and it could be just that not closing the butterfly completely when letting off the gas.

Hope you can help him out, that's all I know.

[Cartmaster]

Lol. Come on now, you have been around here forever, just like me. You know more than you let on!

Oops, time for me to put my tin hat on and duck!

[Texas001]

I have opened the old carb, cleaned a little bit of settlement out of the bowl, used some carb/choke spray, checked the needle and seat to be sure it wasn't gummed up and checked the overall condition of the entire carb. Blew out all the orifices. Looks nice and clean throughout. I do have a question. On the outside, above the throttle butterfly there is a black plastic nob, you can turn that thing about half a turn before it hits a stop. What is that? Does it adjust something? Is there a certain setting. I remember where mine was set so I put it back to that setting but am clueless on what it is for.

I am going to reinstall the original carburetor and see what happens. I was replacing the original because the cart was hard to start and had quit on me. I was just driving along and it stopped. The engine was starving and I had to choke to restart and had to hold the choke out the entire time to get back home. Checked the fuel pump and it was pumping strong. So I blamed the carburetor.

[Cartmaster]

Dont worry about that plastic knob. As these engines are not set up to idle on the EZGO carts, it is basically irrelevant.

As an afterthought, I had assumed you had checked your valve lash. If not, now is a good time to do it as if they are too tight, it can cause the issue you started with. Usually difficult to start, needing a lot of choke to run and backfiring on occasion etc. If you run through all these checks discussed so far, I am sure you will solve your issues.