Strange Idle Issues - 1984 CJ7 4.2L 258 -
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post #1 of 3 Old 09-16-2019, 08:38 AM Thread Starter
1984 Cj7 Laredo
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Strange Idle Issues - 1984 CJ7 4.2L 258

I am hoping someone can help me find the cause of my idle issues. I have a 1984 CJ7 with the 4.2 258. I've done the nutter bypass which made it run much smoother. I've also put on a NOS carb, a new distributor cap, rotor, fuel pump, fuel filter, and fuel line. All of these new parts, in addition, to the nutter, have helped quite a bit.

Even with all of these improvements, I'm still having an idle issue. I believe it has something to do with the mixture, specifically the air portion. If I remove the cover off of the air cleaner, it will not idle at all. If I put it back on, it will idle until I hit the gas pedal. Once I lightly hit the gas pedal, the RPM's drop and it stalls out, but it has no problem starting back up. I've also noticed that if I gently press down on the air cleaner, it will stall out as well. Any suggestions?

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post #2 of 3 Old 09-16-2019, 06:49 PM
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1976 CJ5 
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Sounds like the mixture was tuned with the air cleaner off (wrong). And possibly a vacuum leak.
Doing all of the adjustments doesn't take long, lots of info on the BBD online, including the original Carter manual.

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post #3 of 3 Old 09-16-2019, 10:07 PM
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Stock air cleaner? Thermostatic air cleaner with all the hoses and valves in good condition? Have you plumbed it all as per 1984 or modded it to something simpler?

A 1984 has many feet of hose and fittings that can leak or just plain not work. You MAY be experiencing a vaccuum leak. Can you balance the mixture using the screws alone? Are you getting a drop in revs at less than 1 1/2 turns out?

As suggested ^ idle mixture needs to be set at operating temperature with the choke off and at around 850 rpm, if you cannot get it to stumble at less than 1 1/2 turns, it is because air is bleeding in elsewhere. Did you set the stepper pins in the new carb?

If your revs are set too high at curb idle speed screw, (usually because of problems with the idle), the progression port is uncovered and is adding fuel at idle, hence the progression to partly open throttle will be erratic and it may well die suddenly. The set up of these carbs is sensitive to vacuum leaks and blocked idle tubes.
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1981 CJ7 258ci - Bagusjeep
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1981 J20 258ci - Gladys
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