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post #1 of (permalink) Old 07-24-2002, 10:54 AM Thread Starter
 
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YJ idle oddity.

Did a search, couldn't find anything relating to this...
But here's the deal, it's not a really important problem, but more annoying than anything. I have the timing set to 10 BTDC @ 1600RPM (spec is 9 +/- 2), Vacuum kick idle is set at 1150RPM (Spec is 1100 +/-50) Vacuum solenoid is set at 975 (spec 900 +/- 50) and curb idle is at 750 (spec is 680 but don't remember wat tolerance is allowed, I think it my be 80).
It idles at those RPM's when cold as verified by a handheld tach, but as soon as it warms up (coolant temp over 180 or 190) it will idle at 1150 for about 5 - 10 seconds, will then bypass vacuum solenoid and curb idle and will idle at around 350 - 400.
I've had the hood up and watched it idle like that. You rev up the engine to say 3000, then let it drop. It will then idle at the 1150 I have the vacuum kick set to. While the uppermost adjusting screw (the one that contacts the vacuum solenoid plunger) is still touching the plunger, the idle will drop down to around 400.
The fast idle screw never comes in contact with the idle cam when, nor does the curb idle screw come in contact with the carb. body the whole time.
When I had the carb apart, I did notice that the bowls were a little less than half full, could the idle oddity be caused by not enough fuel in the bowl, or is there something else I should check out?

Only happens when engine is warm (over 180 degrees)
Does this air cleaner on or off.
Carb was rebuilt 2 weeks before I bought the Jeep back in April, was thouroughly cleaned a week ago.
No misfires, all plugs have the normal tan color to them.
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post #2 of (permalink) Old 07-24-2002, 12:55 PM
 
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Re: YJ idle oddity.

I'm guessing you have the BBD, so I will preface all this by saying I am out of my element here... just throwing crap at the wall to see if anything sticks.

You said that it does all these things it's supposed to when it is warming up (still cold), but then acts strange when warm. Most of the time when I have adjusted timing or the carb, I have done it with the engine at normal operating temperature. It almost sounds like you set everything when the choke was still on.
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post #3 of (permalink) Old 07-24-2002, 03:58 PM Thread Starter
 
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Re: YJ idle oddity.

It's not the original carb. but it's a rebuilt Carter.
And no, everything (timing, all the different idle speeds) has been set with the engine at operating temperature - 210+
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post #4 of (permalink) Old 07-25-2002, 05:58 PM Thread Starter
 
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Re: YJ idle oddity.

Alright, here's a little update to my scenario.
Between the time this was originally posted and now I have done the following:

Upgraded old aluminum distributor cap/rotor to Borg Warner "Nascar" type that are brass and not aluminum.
Also swapped out old Mopar plug wires for same "Nascar" brand as cap/rotor.

Ran a jumper wire for the "high altitude" connector under the dash.

Set the timing all the way from 7 BTDC all the way to 20 BTDC in 2 degree increments. (No ping or knock throughout the range, timing is currently set at 10 BTDC)

Checked all vacuum hoses, all flexible and sealed well.

Adjusted carb float so that it sits 1/4" below the top of bowl per the service manual, also cleaned and installed new gaskets on the carb.

With all that, it runs smoother and accelerates better, but still drops to around 450 - 500 RPM after a few seconds of idling. And it's becoming more of a problem than an annoyance now as It's stalled in the middle of traffic 3 times today due to this "idle drop" problem.

I'm really running out of ideas now.
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post #5 of (permalink) Old 07-25-2002, 06:07 PM
 
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Re: YJ idle oddity.

I'm guessing you isolated the vacuum advance when you set the timing and that the vacuum advance source hasn't been changed.

What effect does adjusting the idle screw have after it has warmed up and is performing it's shennanigans?

And where is TR when you need 'im?
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post #6 of (permalink) Old 07-25-2002, 06:13 PM Thread Starter
 
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Re: YJ idle oddity.

Yes, unplugged the vacuum advance from the distributor and also unplugged the wiring harness from the 4" and 10" vacuum on the firewall. Vacuum advance hose is connected to a constant vacuum source (not sure if that makes it manifold or ported.)

The curb idle screw has no effect at all, nor does the fast idle screw. The only one that does anything is the screw that comes in contact with the vacuum kick solenoid and I can eliminate the problem 75% of the time by setting the vacuum kick idle to over 1500RPM. One out of every 4 or 5 times I stop and let the engine sit for longer than 20 seconds, the idle will drop back down to 500 or so.
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post #7 of (permalink) Old 07-25-2002, 10:42 PM
 
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Re: YJ idle oddity.

Have you dont the nutter bypass? That mihgt help if you have not.
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post #8 of (permalink) Old 07-25-2002, 11:37 PM Thread Starter
 
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Re: YJ idle oddity.

No, it's "un-nuttered". Frankly, I've been somewhat apprehensive about doing the bypass to it for fear of royally screwing something up. Though, I did find someone locally who has done the bypass on the same year YJ as mine and I'm seeing what we can arrange to have him help me out with it.
Just out of curiosity, do you (anybody) think that I'll see a drastic improvement with the bypass, or is this a case of "YMMV"?
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post #9 of (permalink) Old 07-26-2002, 05:59 AM
 
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Re: YJ idle oddity.

You will find conflicting opinions from this board on the Nutter By-pass. The biggest issue surrounding it in my mind is if you want to or need to stay emissions legal. Nuttering your carb will simplify your system a bit, and change your troubleshooting. The reason I say "change" and not "simplify" as well is that there is a lot of documentation and other resources (such as mechanics that are familiar with it) available for an engine that is in stock configuration. With a Nuttered engine there is nowhere near as much documentation and you find fewer mechanics that will fool with it or give you advice, but you have a simpler system to troubleshoot.

The biggest thing Nuttering an engine will do is take the computer out of the loop. If you want or need to stay emissions legal, your better choice is replacing the computer (no big deal) if that is where your problem is. If you aren't as concerned about emissions and would like to simplify your engine compartment and have a more solid understanding of what is driving what, the Nutter By-pass may be for you and will probably be the first of a long string of gradual simplifications and cleanups of the engine compartment.

I believe the performance aspects could be argued either way. The biggest issues are emissions and how close to a stock engine setup you want to stay.
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post #10 of (permalink) Old 07-26-2002, 06:41 AM
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Re: YJ idle oddity.

I did the Nutter bypass to mine (87 YJ) and had a very noticeable improvement in performance and smoothness. I too was apprehensive, so I wired it in with a switch. That way I could undo it simply by reconnecting the Vac Adv from ported back to mainfold vacuum, plugging the stepper motor back in and flipping the switch. It worked so well for me I ended up taking out the switch. I used a cheap switch I had laying around, but if I lived in an emissions testing state I would nutter it using a couple of good quality waterproof connectors that let me connect it either way. That way I could un-nutter it for testing in a few minutes.
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