black smoke idling and pumping pedal

black smoke idling and pumping pedal

OEM1984CJ7

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Location
E. Tenn
Vehicle(s)
1984 CJ7 258 w/T176
I did the 2100 swap and TFI upgrade and just now noticing that when idling I can pump the gas pedal several times rapidly and blow black smoke out the pipe. Engine will almost die but doesn't and puffs pretty good. Once you rev it a couple of times and idle it over about 1200 rpms it clears up. It runs great while driving and revs great under normal conditions, but if you just pump the pedal you get black smoke. It is on a AMC 258 i6 / 4.2l and manual choke. I check the choke cable to see if it slipped and it is all the way off and engine is normal operating temp. Trying to figure out an accurate way to figure mileage also as these gauges are pretty sloppy. Maybe an inline fuel flow meter and measure after driving 50 miles or so.

any ideas? I don't want to start messing with the adjustments screws just trying to see if anyone knows what would cause this.

thanks.:D
 
It just sounds like you are running rich. Time to start adjusting screws :D

When you did the TFI did you regap the plugs to .045?
 
Carb may be dripping fuel interally. Dirt or rust from the fuel tank may be the cause.
 
Yes, regapped the plugs to .045 and just pulled the fuel tank to unclog a vent line and replaced sending unit while tank was down. Flushed tank/cleaned before re-installing. I figured it might be adjusting time but I am not really a carb man. Any ideas for the best place to find instructions on how to set jets? I read many prior post and really confused now.


Jeepbrah: Why might it be the head gasket? I don't have any leaks.

Just curious.
 
Take a look at the position of the linkage to the accelerator pump. If it runs well under normal conditions and rich when pumping rapidly this may have something to do with it.

The patient tells the Dr. "it hurts when I do this" and the Dr. reply's "well, don't do that". Is there some reason you need to pump the fuel several times while driving??:cool:
 
I'm with IO, but if you think you have a problem with the carb buy a rebuild kit and get some experience. Not that bad.
 
It just sounds like you are running rich. Time to start adjusting screws :D

X2 on time to adjust the idel mixture.
If it only does it when your pumping the gas then Im with IO, why do you have to sit and pump the gas?
 
I have a co-worker that is bringing a vacumm gauge to work tonight and said he can adjust them. I am not just sitting and pumping the gas pedal just for the heck of it , I am simulating taking off from a steep hill but sitting still so I can actually see the smoke. The carb is newly rebuilt and I bought the kit off fleebay from the guy in CO who has sold thousands of them and had the jets preset and my mechanic that set the timing said he adjusted the carb and it blows smoke ever since.


thanks.
 
I still don't see the idle adjustment causing this but I been wrong before.:D
 
JeepBrah mentioned something about a head gasket.. I am starting to wonder now if that may be the case. It is loading up the carb when the jeep is under a load ( going up a hill) doesn't feel like the compression is there. Also, If I shut it off and immediately restart it does fine. If I wait 10 min or so it wants to turn over several times and then acts like it is flooded but starts. Could this be because the compression is leaking down from the bad Head gasket???

Just trying to throw everything out there. Also, when I run it at high rpm's and shifts I am now getting a slight white smoke when shifting that I was not getting earlier.

Hmmmm...


Any thoughts on this?

thanks.
 
do a compression check, you can rule out the head gasket, but im pretty sure you have a fuel delivery issue. Its possible you got a wore out, bad carb for the conversion, the first one i got was bad (well it had been "modified" for a dirt track car) and it was doing basically the same thing, mine would overload at idle but run great at high speeds, and it would run kinda crappy pulling a hill like it was dumping to much fuel in when it didn't need it. you can play with the accelerator pump linkages to change how much fuel is given and how fast when you press the accelerator, you can also change power valves, holley power valves work in most years of the mc2100. when you done the swap did you check to make sure 1.08 is stamped on the side of the carb, anything bigger could be causing your problem as well.
 
Last edited:
I still think it's the carb. Float my be set too high
 

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