89 YJ stalling, backfiring mostly for startup

jj2000bc

New member
1053863

I'm having a problem with my YJ stalling after starting for a couple minutes and then stalling when i'm at a light. I've just done a bunch of new work to it. including a bypass for the computer with the stepper motor no longer in the equation. I ajusted my carb to the spec's again, and it still does this. Then I cleaned the venturi's as well and replaced my old coil with a new accel super stock and replaced all the spark plugs. Anyone have any suggestions.
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1053864

Double check your timing. Make sure you didn't cross any plug wires. If these two check out you might try a fuel volume test. If you have a manual it should tell you how much fuel should be pumped out for a given time. But I suspect timing mostly. Good luck.[addsig]
 
1053866

Did it do this before you did the work? If so I would say that it is something other than what you did. If not, check the wiring like Cardoc said. Also- is your Jeep auto? If it is then it may be your transmission not downshifting and stalling out the motor at redlights and such. But if you are stick, then obviously this doesnt apply. I would start with the timing and make sure its all ok.

Backfiring is usually from a cyc. not firing and sending the fuel/air mixture into the exhaust where the heat from there ignites it. Again comes back to a timing issue-[addsig]
 
1054140

I have all wires in correctly. I just redid the timing again. the backfiring stopped. I'm now working on the idle again, but it's hard to get the mixture right. when i redo the idle mixture screws it seems to get better, but it still doesn't idle nicely. how do i get my jeep to idle properly now??????? sometimes when i put the idle mixture screws in too much it stalls again. and when i screw them in it idles really eratic. [addsig]
 
1054149

As simple as it sounds, check the hot air vent that comes from the the exhaust manifold and goes into the engine, it's right in the front, a foil tube that has hose clamps on it. I went offroading and on the way home it was stalling at lights, it wouldn't idle, and it was just the tube!
Good luck man![addsig]
 
1054155

This may sound like a dumb question, but how are you starting it?

Are you starting it by repeatedly keying the ignition while holding down the gas, or are you giving the carb time to get primed before keying the ignition.
The reason I ask is that this is what I was doing when I first started driving my jeep, not knowing that this was not good for carburated enines. What it leads to is the carb flooding while warming up the engine. This caused alot of sputters, stalls and backfiring for me ONLY during startup and warmup.

If you are starting it correctly for a carb'ed engine, I'd venture to guess that either your carb may be running rich or your timing might need some adjustment.



edited by: chinard, Feb 07, 2003 - 11:02 PM[addsig]
 

1054629

I have a 90 YJ and it had the same problem that you're describing. There are 2 things I can think of (by the by, my carb is non stepper-motorized):

1. Vacuum leak - especially with the hose that goes from the manifold to the vacuum advance on the distributor. (The hose is right there next to the carb). After cleaning out the idle pickup tubes and venturi cluster, just like you, I still had that troublesome problem with proper idling and stalling. The problem was right there in front of me and never noticed it until I looked under the hood in bright sunlight. That hose just wasn't connected to the vacuum advance on the distributor.

2. My engine would stumble and eventually stall out when I noticed I pressed down on one of the wires on the ignition coil connector to the ignition coil tower itself. I made sure the wire was kept up so it wouldn't touch

edited by: MadMiracle, Feb 11, 2003 - 01:27 PM[addsig]
 
1054668

If your still using the stock carb it is probably the choke. I have an 88 yj. I did all those cleaning tricks and rebuilt the carb but still had problems. I replaced it with a Weber, it still idled rough a little, then I did the nutter bypass, a little better but great, until I switched to the juice box. A bigger dist cap 30,000volt coil and 8mm wires. starts up and runs in 1 turn. even when it is below freezing out! Hope this can help![addsig]
 
1054692

Hey guys, thanks for all the help. just an update on the situation. The problems that i'm having now is only for start up, it stalls or has a hard time starting. I'm looking into getting a timing gun, since going by sound isn't always the greatest, and not very accurate.

Choke is fine. it works very well. I even made sure that the pvc valve is working and there is a ton of suction.

I turned back the two idle mixture screws in all the way then turned them out (3) full turns and then turned the curb idle screw in (2) full turns. well aparently what's happening, is when i punch the gas the engine hesitates, but it has a nice sounding idle, but still at the 1100 rpm range. if i turn the idle mixture screws in so they are only 2 or 2 1/2 turns out then it runs nice and the hesitation goes away, but then it doesn't start up. I then have to give it gas when i'm turning the engine over.

when i usually start up the jeep i punch the gas once(to position the choke) then start up the jeep without having my foot on the gas.

Any suggestions????

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1054768

Sorry this post is so long-winded:
I have the non-stepper motorized Carter BBD 2bbl carb in my YJ. I believe that stepper motor is there to control the metering pins that adjust the fuel mixture according to the oygen sensor, which is controlled by the computer, but you've done the Nutter bypass?
I don't know much about that.

I have metering rods in my carb which are controlled by a vacuum piston contolled by a rod metering cam slid and screwed down into the accelerator pump lever which runs through the bowl cleaner of the carb.

For a very short while, I'd have to floor the pedal while turning the key to get my YJ going. I can't remember what I did to overcome that. I believe it only happened to me when the engine was warm. I knew my choke and choke plate weren't working the way they should. I may've adjusted the carb thermostat choke cover to 90 degress rich from the index mark with a cold engine until I got some spring tension to close the choke plate, but I think that was for another reason. I did all of this after adjusting the idle mixture screws when the engine was at max operating temp.

One question: When the engine is warm, do you start the engine by pressing the gas pedal halfway down, or do you start a warm engine without any sort of pressure on the gas pedal at all? With a warm engine, If I remember correctly, I'd hold the pedal halfway down (according to the owner's manual that's what you're supposed to do), but that would give me that problem of having to floor the gas pedal (again, if I remember correctly). This is for sure with me: with a warm engine, I just start the engine without any pressure on the pedal and that works fine for me.

Alot more questions: Are you revving the gas while holding the key turned to crank the starter motor until the engine finally fires up? (If you do, that might damage your starter and/or your ring gear on the flywheeel). Or, are you turning the key again and again and again until it finally runs? If so, do you pump once before every turn of the key? If that's the case, you might flood the engine with gas and that's no good.
Also, do you let the engine completley warm up before driving to see if the engine hesitates. When my engine is cold it will idle nicely and hesitate while driving, but only if the engine is cold and the engine hasn't reached it's max operating temps. I ususally let my engine idle until it finally does reach max. It's a smooth ride from there.

As a process of elimination I'd suggest setting the idle mixture srews back to where you can start the engine normally again and let the engine warm up completely, and then see if the hesitation goes away. What I think is really happening is that when you hit the gas, the fuel is sprinkling from the carb into the intake manifold rather than spray-jetting. Vacuum leak maybe? As thinks heat up, the carburetor gaskets expand more than the metal in the carb, therefore sealing any leaks.

The only other thing I can think of is the float level in the carb needs adjusting.
Try this link Carb Trouble-Shooting

edited by: MadMiracle, Feb 12, 2003 - 08:25 AM[addsig]
 
If you have the stock carter. Get rid of it and get a mc2100. Its well worth the $130 ..I did it and it gave me alot more power and the idle is unreal..
 
i also have a 89 yj thats ...did the comp.bypass same problem ...starting is goood but no back firing for me ... but did have intake leak at the head on 6th cylinder ....could br the problem ...for start up ...but my yj would run good after warm up...when its running spray some brk kleenz around the intake and carb see if it sputters or stallz out.....also cleaning out venturies(this is whst i've found) doesn't work as well as drilling out the tubes a hair larger ...some better plugs could be the answer?? i use champion truck plugs with a bit larger gap....too much fuel not enuf spark...
 
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