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-   -   rough idle (http://www.wranglerforum.com/f218/rough-idle-68013.html)

dmwilson01 11-07-2010 12:08 PM

rough idle
 
well a few weeks ago my wife bought me this jeep and it is in great condition but the guy she bought it from wasnt to handy and allways had to take it places to get the oil changed. so i replaced the valve cover gasket rebuilt the carb (mostly) and replaced the spark plugs and wires the cap and rotor look good i sanded them a little and tried to time it. i get really crappy idle and i have to set the idle to like 1500 rpm to keep it running but when i get out on the high way it runs fine. I went on line and someone said and i will coppy and paste

The Jeep 258 (4.2L) I6 isn't a power house, but it has gobs of low RPM torque that makes it a great engine off-road. The most common problem I see with the engine is it's inability to idle. Between the 258 in my '81 CJ-7 and a couple friends that have 258 equipped Wranglers, I have fixed this problem half a dozen times and the cause of the problem has always been the same. The problem has always been caused by clogged idle tubes that cause fuel to drip out of the venturis and make the Jeep run rich at idle. Fixing the problem is relatively easy and once you get past this problem, you will get much more enjoyment from the 258 and the Carter BBD carburetor.
The Carter BBD is a two barrel carburetor that was available on late 70s to late 80s Jeeps with the 4.2L engine. There are two variations of the carburetor, one is computer controlled and has a stepper motor on the back side. The computer controlled version was used after 1981. Other than that, the two versions are the same although it seems the stepper motor version is a bit more troublesome.

The Symptoms

The symptoms of the problem include stumbling and sputtering at idle. In advanced cases, the Jeep will stall at every stop sign and will only run at high RPMs. Gas mileage will suffer since fuel will just be sloshing out at idle. Sometimes the idle will be turned up to a high RPM to avoid the problem. Typically, the Jeep will run fine at higher RPMs (unless there are also other problems.)
For a sure diagnosis, park the Jeep with the engine off and remove the air cleaner cover. There should be a plate over the throat of the carb, the choke plate. If you open the choke plate you should be able to see down the throat of the carb and you should see two screws with holes in the middle of them. Next to them are two passages with a nozzle in the middle of each. This thing is known as the venturi, when air passes by, fuel is supposed to be drawn out through the nozzles. If the idle tubes are clogged fuel will drip from those nozzles during idle.


he then goes into how to take it apart and use some wire to clean out the idle tubes. so last night i went and took part of the carb apart and it was all clear and nothing i could see was clogged so i put it all back together and it was still dripping out of the venturi nozzels. ok i guess what my big question is when i rebuilt the carb i couldn't remove the idle fule mixture screw caps after about an hour i got pissed and put it all back togher so they were not adjusted ok and the second it has an electric choke but it doesnt work so it's hard to get this thing to stay running when it gets warm. i know it's an easy replacement and all i just don't quite know where to start from. and i was considering doing the nutter bypass but i want to get the dang thing running first before i go cutting wires . anyway if anyone takes the time to read all of this and has any ideas of where to start i would greatly appreciate it. OH and also i think the carb is a carter. and i don't have much money to replace it with a weber or some 2100 carb.

dmwilson01 12-11-2010 01:45 PM

update
 
I found that I didn't set the travel of the metering rods. fixed that got the idle mixture screw caps out and adjusted as well as i could and I messed with the timing. it runs great at high way speeds but at idle it has a miss. I did some more research and I think it has a vacuum leak on the carb at the throttle. I think that the hole that the linkage goes into the carb is oval. is there something out there like a brass bushing I can put in to make the hole round again that wont wear out like the aluminum? if anyone knows of anything please let me know.

scott howard 12-11-2010 02:37 PM

you could machine a bushing for it.
but you really should do the nutter bypass.
This is a Picture Guide to Nutter Bypass - JeepForum.com

dmwilson01 12-12-2010 08:52 PM

continued
 
i have the wires to do the nutter bypass. i just haven't had time to go work in the garage that and it's getting colder. but i will do it. i thought about going to a machine shop with some measurements of what i need. but i was worried about messing up the the placement of the shaft and messing up where the butterflies meet the base of the carb. but i guess if i took it somewhere and had them mill the hole out exactly rather than me try to use a drill press on it. i do greatly appreciate the input on this. if you have any more ideas please shoot them my way.

scott howard 12-12-2010 10:16 PM

ask the folks on here if they have a non emc controlled carter carb laying around that you could have or buy that is in good shape and do the nutter by pass .
i bet you will find a few to choose from.
and use it while you save up for a mc 2100 carb.


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