'85 CJ7 6 Backfires on downhill idle

R

Redi85CJ7

New member
New Carter Carb on this 170K straight 6

I noticed the spray-carb-cleaner-on-vacumm-connections-look-for-leaks procedure posted on another thread,
so will try that.

Also having difficulting getting a proper idle.
Keeps changing and after significant run time, stalls on stop.

All suggestions appreciated.

C
 

Could be a million things bud. Check vacuum leaks first, then clean and tune that carb real good. Make sure everything on the outside of the carb is in good shape too, the choke and throttle linkage is all in good order and lubed. While you're in there, maybe check the plugs, wires, and other expendable ignition components and see what kinda shape they're in. Just running through the list. If none of this works, hopefully you'll discover some other symptoms along the ay that may help disgnose your problem. Good luck!
 
Another way you can check your vacuum is to just go get a plug kit from autzone and plug all the lines out of the carb. The CJ needs none of them to run and would immediately tell you if there's some problem with vacuum. Don't leave it like that though...
 

Thanks for all the input.
Tried new plugs rotor and cap but no help.
I'll be searching this forum for a previous answer,
but maybe someone can suggest an alternative to the Carter Carb.
thanks
 
If you have no vacuum leaks, check the float level. Most carb performance is directly related to float level. To low of a float level will run the engine lean, giving you backfiring and upfiring sometimes. An alt. to the carter would be a holley. Very low maint. and they have specific units for offroading that can handle fuel slosh in the bowls. Just don't go with an oversized carb. Bigger is not always better. A smaller carb will give you more air velocity, and pull the fuel better through the carb, with better low end torque. A larger carb will bog you down, and have no throttle response. Good Luck
Guysmiley
 
The Carter is brand new, so , Cduemeg, I think clogged venturis may not be the problem.
I think I need to try the second vacumm test.
But, it seems that the vacumn selonoid (probably not the name) the unit with the piston that is supposed to raise the throttle level at appropriate moments, is not working. Doesn't seem to do anything.
Guysmiley, is that float easily adjustable? and is the factory setting likely to be low?
Also, you mentioned Holley as an off road carb, do they have a street version smoggable in CA?
I looked at the e-bay guy who's rebuilding Motorcraft carbs. any comments on that option?
Thanks for all the attention and help.
 

alot of people will tell you to pull the carter and put on the motorcraft 2150 carb. i myself have done it and it works great. if emissions are something you can get by on its worth the $100 to do.
 
slo-wrench44 said:
alot of people will tell you to pull the carter and put on the motorcraft 2150 carb. i myself have done it and it works great. if emissions are something you can get by on its worth the $100 to do.
Click to expand...

From everything I've read, I'd estimate 90% of Jeepers prefer the Motorcraft 2150 over anything else for both on and off road performance. I can't speak from personal experience, having the EFI, but I'd have to agree with slo-wrench on the Motorcraft, having read plenty-o-reports on it.8)
 
Yes, I've heard much about the Motorcraft. Slo-wrench44 you mention the MC2150 but your profile indicates MC2100. Is there a difference? You also mention $100. The E-bay guy is charging close to $300. Where does one get a $100 unit? Also, from your profile it seems you're a full tilt mechanic. Could an ameteur replace the Carter. Finally, are their smog issues with the MC. I'm in CA. Thanks for the helpful responses.
 

MC 2150 is the higher altitude version of the MC 2100. Pretty much the same carb. Just keep looking around. Decent junkyards will be full of MC21xx for cheap and even eBay should be. The carb swap was a cinch, even I did it. Just read a lot of online writeups (google is your best friend). About smog, I'm pretty sure it'll pass as long as you got it running well. I don't know for sure, but have not heard otherwise, so I'm giving the carb the benefit of the doubt. I'm relatively vertain it will pass though. If not, you can run one of those additives that gurantees good smog through your tank every time you go in for an inspection :). Good luck bud, and keep us posted.
 
I've had some progress in this Carter Carb saga.
Was able to have the Jeep smogged (CA)
Had vacumm lines checked.
Runs pretty good except idle.
If you can spare the download time please
see
http://www.thecriticalcrab.net/consign/jeep/carter_carb_idle

You can hear my CJ7 start and idle
or more accurately... not idle.

seems like this must be a sensor or something.

Advice and recommendations appreciated.

C
 

If there is no vaccum problems, it may be sucking in air somewhere else. Either where the carb attaches to the manifold, or where the manifold is attached to the block.

Have you followed the procedures for tuning the carb? The backfiring sounds like it is dumping fuel into the engine and loading up the cylinders with gas. When it stalls, are the plugs soaked with gas?

How is the ignition system? I had an intermittent problem with the ignition box of mine (usually when damp).
 
Have you followed the procedures for tuning the carb? The backfiring sounds like it is dumping fuel into the engine and loading up the cylinders with gas. When it stalls, are the plugs soaked with gas?

How is the ignition system? I had an intermittent problem with the ignition box of mine (usually when damp).[/QUOTE]

Where will I find tuning carb procedures?
Though I'm not so concerned about the backfiring right now, but more the idling problem.

Ignition system seems fine as it starts immediately.

thanks for you response.
C
 
Here is an article on replacing the carb on 258s
carb replacement

I don't know if this will help you or not since your carb is new.
carter idle problem

Do you have a service manual? They have the adjustment procedure.

You start by running the adjustment screws all the way in (don't bottom them hard), and turn them out a set number of turns to start with, then go from there. I don't have an older manual handy, or I could look it up for you.
 

Replacement may be the answer.
Had I done my research in advance, I would have installed a MotorCraft.
May still be required.

I've seen the article to which you refer, but as you say
my carb is new so I think it's not applicable.

Your adjustment tips are helpful and I'll give them a try.
I have an older manual that came with the vehicle.

Were you able to see/hear my idle movie?
The fluctuates by itself rather dramatically. It's not just that it dies.
Seems like it must be a sensor of some kind.
Sometimes it even idles fine.

Thanks for your help Jeepr
 
Last edited:
jay79cj7 said:
Stalling on a stop is a symptom of clogged venturis on a Carter carb. Check the how-to section.
Click to expand...

Exactly. The venturi tubes are too small. You can correct this by drilling them out. It doesn't make the crappy Carter a great carb, but it will allow it to idle.

See this article:
http://www.off-road.com/jeep/tech/engine/carter.html
and note this important detail:
To avoid repeated clogged idle tubes, drill out the idle tubes to 0.032". This will greatly reduce the frequency of clogging and it is a procedure that was actually recommended by Jeep for a while.
Click to expand...
 
I got your video to play. I think you should start by checking your timing. then adjust the idle mixture adjustment screw (might be a screw with a spring on it). Turn the screw in and lightly bottom it, turn it out 1.5 turns, and adjust it in and out till you find the highest RPM. On the original carb the adjustment screw would have been under a dowel that needed to be drilled out. If you got a new carb, it should be exposed.. (cross your fingers)


I listened to your video again, when you bump the gas it would put the carb on high idle. When you hit the throttle again after it's running, it drops the carb off the high idle. It definately sounds like you need to adjust the carb.
 
Last edited:

Thanks for the input and for watching/listening to my video.

I've taken out the idle tubes and they are already 0.032 .
I guess these are the venturi tubes (see attached pic).
Hmmm. Was hoping that would be the quick fix.
Not sure whether to make them even bigger or not.
Comments on this appreciated.

Once I put it back together I'll try adjusting the Carb.
However, when I had it smogged I had the mechanic check the timing
and adjust the carb.

If I keep the rpms up over 5K it seems to idel tolerably, but below that
no go.
 

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