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Unread 01-06-2012, 06:46 PM   #1
BuckleshootCJ5
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Quadrajet idle question

I can't get my engine to idle below 800 rpm with the advance at 12*.

The carb is a quadrajet ('77 not original to the motor or Jeep) with a recent carb kit done on it. It is manual choke. I have carb sprayed for vacuum leaks. I recently upgraded the ignition and all is good there.

The engine idled high before the carb kit and ignition upgrade.

The issue is... The idle screw is backed off to the point it is not touching the throttle linkage. The linkage can't go any further forward.

At 12* advanced it idles at 800. At 10* it idles at 700. At 8* it idles at 600.

I would like it to idle somewhere between 550 and 650. Not sure yet, cuz I haven't got it there.

You might ask now, if it idles at 600 at 8* advanceda then leave it there. I would, but it doesn't run good there. It wants to bog down, especially in 3rd and 4th gears.

It runs best through the gears at 12*, but it is idling at 800 when I have it there.

Right now I have it at 10* and idling at 700. It runs good, but is a little sluggish.

So my question is... What the hell can I do to make this thing idle around 600 with the timing set at 12*??? Is it the high idle screw? I haven't messed with that because I thought that had to do with the choke???

When I did the carb kit, I took pictures of the choke linkage and am pretty sure I got it all back together the same way. Of course maybe it was messed up to begin with and I put it back together messed up. Not even sure if this matters, cuz the choke works fine. Is there something else on the passenger side of the carb that could be wrong???

For what it's worth, here is a pic and thanks in advance for any pointers...

[IMG][/IMG]

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Unread 01-07-2012, 09:51 AM   #2
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Bump for some suggestions...
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Unread 01-07-2012, 12:58 PM   #3
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Unless you want it dying during tricky maneuvers keep the idle around 750. 550 is way too low IMO and backed up by your observations about how it behaves in the higher gears. You're getting too much rpm spread between the idle circuit and the running circuits. Engines don't rev up well on the idle circuit, you need immediate transition to the run circuit to rev cleanly, not a 200 rpm gap.

good luck
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Unread 01-08-2012, 10:03 AM   #4
BuckleshootCJ5
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Thanks and I get what you are saying, but...

I would like to be able to set the advance at 12* and have the ability to drop the idle to around 600 or so. I think it would run the best then and also give me the choice to just turn the idle up to 700 or so when wheeling.

As it sits now, if the advance is at 12* it idles at 800. I don't do much winter wheeling, but I do like to putt around town in the Jeep during the winter. Just to keep her "alive", I make short trips a few times a week. Like running to the parts store, picking up the kids, etc...

I guess what I'm saying is that I'd at least like to have the "opportunity" to adjust the idle when the timing is at 12*...
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Unread 01-08-2012, 07:13 PM   #5
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A rig with a manual should idle just fine in the 550 range.
Insure there isn't another problem.
Insure the choke high idle is completely disengaged.
Inspect all linkages and curb idle screw to insure the throttle shaft isn't hanging on anything.
Pull the carb to insure the plates aren't hanging up on the gasket/manifold.
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Unread 01-08-2012, 07:21 PM   #6
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What is the normal operating timing? did you take off the vacuum line when setting it?
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Unread 01-08-2012, 07:25 PM   #7
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I do know if you advance the timing to much your idle will increase. Be careful if your advancing your timing i would say 2-3* over factory you will need to run higher octane fuel or you will detonate and get the pinging sound under load
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Unread 01-09-2012, 05:00 AM   #8
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Quote:
Originally Posted by oilfieldhand View Post
I do know if you advance the timing to much your idle will increase. Be careful if your advancing your timing i would say 2-3* over factory you will need to run higher octane fuel or you will detonate and get the pinging sound under load
Not really. While advancing the timing will up the idle, it should be curable with the curb idle screw. In the end, loosening the curb idle screw should close the plates enough to kill the engine.
It is also common practice to bump the timing up to help fuel economy. This rarely requires a switch to higher octane fuel. A rule of thumb is to advance it till the engine pings under load, then back it down a couple of degrees.
Again, check all your linkages, choke idle adjustment, and insure the plates close completely with the curb idle screw disengaged from the stop.
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Unread 01-09-2012, 08:04 AM   #9
Foundrydude
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If the blades are closing tight then you've probably got loose throttle shaft bushings.

An adjustable vacuum advance can would be another route to cure the driveability issues in the higher gears.

good luck
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Unread 01-09-2012, 08:31 AM   #10
swatson454
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Can you bring the idle speed down with the mixture screws without showing any signs of a lean condition? Don't some of those Q-Jets have basically an idle air bypass adjustment on them somewhere? Also, is it possible to close the secondaries a hair? That might be your ticket.


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Unread 01-09-2012, 03:32 PM   #11
jeepdaddy2000
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Quote:
Also, is it possible to close the secondaries a hair? That might be your ticket.
Good point. I got so caught up with the primary side I forgot about the secondaries.
Check to insure the secondary shaft moves smoothly and the plates are not binding on the manifold/gasket. They should be completely closed.
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