4.2L runs rough at idle and dies when throttle applied - JeepForum.com
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post #1 of 3 Old 10-22-2009, 02:06 PM Thread Starter
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1984 CJ7 
Join Date: Oct 2008
Location: Tyler
Posts: 99
4.2L runs rough at idle and dies when throttle applied

Hi jeep guys/gals, Im the proud new owner of a 84 CJ-7!! After driving it home for 2.5 hours, and driving it to work, it decides to run like crap on me when I try to leave. It will start, run really rough at idle( like the back of the motor is bouncing 2 inches up and down), and whenever I touch the gas it will die, or if I shift into gear and it gets a load from the transmission it dies. Its got a 4.2L/400/300 for a power-train, with a (crappy from what the previous owner told me) carter carb. Carbs are not my forte, especially ones with 20 damn vacuum lines running everywhere. Any suggestions on where to look?

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post #2 of 3 Old 10-22-2009, 02:18 PM
Mike Romain
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1986 CJ7 
Join Date: Nov 2007
Location: Off the Grid in Chester Grant
Posts: 18,083
The carb can just purr with a $15.00 kit in it. The kits are easy to put in and have the settings.

You may have gas filter issues, they plug up fast after the Jeep sits for a while usually, but it more sounds like a choke issue.

To see if the choke is working, when off open the air filter and be sure it is closed after giving the gas pedal a shot to allow the fast idle to set. Then watch as it warms up. you won't be able to go until that choke is fully open, autos suck that way.

These engines need a shot of gas or two or three depending on how cold it is out, then you use the key to start it with your foot off the gas. The choke and fast idle should then be on. When the rpms come up, you tap the gas pedal, then you wait for the rpm to come up again and tap again. Eventually it will be warm enough to go to curb idle and you 'may' be able to put it in gear and drive away without is chugging, they like to be really warmed up, 5 minutes + and the choke is a timer that comes off too fast usually. I went manual choke, much better in my opinion.

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post #3 of 3 Old 10-22-2009, 03:44 PM Thread Starter
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1984 CJ7 
Join Date: Oct 2008
Location: Tyler
Posts: 99
ok thanks! I understand fuel injection no prob, but carbs are a little confusing to me. I went out after the jeep had sit for a few hours and pulled the air cleaner, the choke plate was closed, started it up without pumping the gas and it fired right up smooth as can be. After about 5 minutes it was open, and the motor revved up without problems. I didnt do anything, but the jeep runs great now....lol Before the choke plate was fully open all the time, maybe it just wasn't on last time.

oh and what is this kit you talk about? carb rebuilt kit?
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