Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: MP81 on October 19, 2017, 05:40:43 PM
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Hi there,
So as of a week ago, I went to move the car ('81 Z28, LG4 305 - CCC Q-Jet) around (to test an issue with the speedo cable I was having) and I noticed the car was smoking pretty heavily at idle - not blue smoke, a faint gray smoke with some black in it. And it did not smell like oil at all - definitely smelled rich as hell.
I just started it today (to test my fix to the cable) and did confirm it is absolutely running insanely rich (pretty sure it's spitting raw fuel out of the tailpipes), and after pulling the car into the garage and getting it positioned (tight garage), even with the garage door open, it was nearly impossible to stand inside without your eyes and nose stinging. The car is idling quite high too, and if you give it throttle it's hesitant to climb (bogging, I'm thinking). The smoke is not just at idle, it also smokes if you increase throttle as well... The insides of the tailpipes are black, and I've only put about 70 miles on the car since installing the new exhaust.
Thing is - it wasn't doing this a few weeks ago, after I got the headers and dual exhaust on, or anything (little smoke, but that may be valve seals, or just the forming lube).
Is the float stuck? What could cause it to suddenly run so insanely rich, all by itself?
I'm thinking the carb is looking like it needs a full rebuild - or is this something simple I've overlooked?
Thanks!
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i would check the choke pull off and see if it has developed a vacuum leak , push it closed hold your finger over it and see if it stays if not its bad fwiw
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Would that cause it to run that rich though?
Is it possible to pull off the top section of the carb (on-car) to see if the float is stuck?
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yes it would pul the air cleaner and see if the choke is opening all the way if it is that is not your problem . yes you can take the top off with it mounted on the engine i don't like to bend over that long i like to work on carb on bench . you should be able to tell if float is stuck . shut off car and look down carb ,you should see gas running down the intake . fwiw if the carb has never been apart buy a good kit from cliff and rebuild it so you know what you have . make sure you keep track off all the adjustments so you have a good starting point to tune .that carb has electronic metering rods you may have them stuck open .
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Idling too high and running rich is most likely related to the choke pull-off or electric choke. Check those items first. If the float has failed it would flood out and not run at all.....Cliff
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The linkage coming out of the pull-off (I think) seemed extraordinarily sloppy when I was playing around with the carb the last time...I don't recall it having so much play before, but I can't say for certain that I messed around with it prior.
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did you somehow unplug the choke ? once you take the air cleaner off and fire up the car you will know soon whats wrong open the choke by hand with it running and the car should run fine .turn the key on for 1 minute before you start the car and the choke should start to open a little if its working correctly.if its working and you start the car and it doesn't open all the way in say 3 minutes depending how cold it is.ether the pullout is bad or your vacuum hose going to it is unplugged or bad .fwiw
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Didn't unplug it - I did check that. I crimped on a new connector (the stock one was long gone) after putting the headers on, real tight fit on the spade.
I will check to see if the choke is opening all the way, hopefully this weekend. It'll be in the high 40s so it might take a touch longer.
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Started it up today - this is as far as the choke blade opened after running for about 5 or 6 minutes. By the time I shut it down, it was idling up near 2k, and revs were real slow to come down when I did rev it up to try and get it to drop down.
It was still smoking, but didn't seem as bad as the last time, maybe because it was colder out? May have been a placebo effect, too.
The vac hose is still good between the pull-off and the carb.
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Replace the electric choke. It should be fully open in about 2-3 minutes. We have USA made ones on the website, and they come with a new connector for the wiring harness......Cliff
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That probably has been the cause of the idle issues all along. They went away in the summer, since it was warm out, the coil probably worked properly.
Maybe it's how it is designed to work, but if I were to pull, manually on the choke blade linkage, it would stay down until I opened the throttle blades.
So, replacing the choke should likely solve the rich issue as well as the funky high idle and slow rev drop?
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How tight do you have the choke set? I set mine so they just close at 65-70 deg.
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No idea - I've never adjusted it.
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couple of things . do you have good voltage at the chock with key on or running ?also is the car running in the photo? if it is your pulloff is bad fwiw
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I did check for voltage at the choke, and if I recall correctly, I did have it.
And no, I took the picture just after turning the car off.
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So I got the new choke the other day and decided to put it on today.
After installing, it exhibited the exact same symptoms as before - running stupid rich and at high idle. So I decided to replace the connector - the voltage readings I got were hit or miss on the terminal, but were fine at the wire.
Put the new pigtail on, and as soon as I keyed on, the choke closed entirely and now the car won't start at all.
I made sure the fast idle cam (I think it is) was inside the enclosed part of the "tang" of the clock spring, and then rotated back to roughly vertical (so the connector is on the bottom, as my other choke was). Did I need to rotate it more or something? Or is that how it's supposed to be - I do remember the choke plate at cold start being closed prior to all this goofiness (maybe the carb was flooded from it running so rich just a few minutes prior).
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Just leave the key on for a minute or two as the engine is warm enough it isn't like the fully closed choke flap.
Also verify that the pull-off is unloading the choke correctly on a cold start.
The basic setting for the new choke is to install it and rotate counter-clockwise unit the choke flap just fully closes. There is a fine line on the choke that should be at or close to the center mark on the choke housing and well within range from rich to lean.
Make sure when adjusting the choke that the throttle is open some or the fast idle cam/linkage may prevent the choke flap from closing......Cliff
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So I went ahead and set it up that way yesterday - turned it just until the choke flap closed. This put the mark (on the top of the choke) within the little set of dashed marks. My original choke had the line at about the 2 o'clock mark, computer to 12 o'clock, however, so the choke did not appear to be rotated by about 45 degrees (where the connector sits, was right at 6 o'clock compared to about 8 o'clock now).
The car did start, so it was probably just flooded, but that choke never opened more than 1/4" of an inch. How would I know if the pull-off is causing this (or could it not)?
I measured voltage at the connector (I believe this is the factory choke wire) and I got right around 10.5-11V.
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The choke pull-off unloads the choke at initial start-up, it has nothing to do with how the choke is adjusted.
Vacuum test it to make sure it is working?
I would also test the electric choke by grounding it on a negative battery post and attaching a positive wire to the connector from the positive post. It should heat up in about 2-3 minutes and the coil will move so reference the initial position and watch it move as it heats up.
Once you verify both parts are working put them back in place and set the choke so it just closes the choke flap. Make sure the throttle is open so it can do this or the mechanism will lock out the choke and prevent a correct setting.
Once the choke flap is fully closed apply the pull-off with a vacuum pump or just fully compress it by hand. The choke flap should open some or it will need correctly adjusted as well. It only needs to open enough so the engine doesn't flood out on a cold start, and can be fine tuned to perfection with a little effort if you move quickly after the engine initially fires up.....Cliff
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I meant more that can the pull-off prevent the choke from opening?
It does seem to have proper vacuum as you can only move the pull-off in/out after the engine has been off for a while and the vacuum bled off. Otherwise it's not really possible to move.
The choke flap does open some, so I don't think the pull-off is causig my issue - but rather a choke only getting 10.5-11V not heating up fully - though I'm not entirely sure how that suddenly is a thing (voltage at the battery is fine).
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The pull-off should be easy to fully compress with the engine off and it should hold vacuum.
When released it should fully open in about 2-3 seconds.
If it is difficult to move or doesn't release quickly it needs to be replaced....
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I'll check that. Could that not allow the choke flap to open fully, or would it cause other issues and not that?
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The pull-off only unloads the choke flap on cold starts and unless something is bent it will NOT contact any parts of the fast idle cam or choke linkage to prevent it from fully opening.
The electric choke does the rest, and the flap should be fully open in about 2-3 minutes, depending on how you have the electric choke adjusted.......Cliff
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Finally got around to checking - I can compress the pull-off when the engine is off, so that seems to be fine.
Ran a wire right to the 12V terminal and in a few min, the choke blade was all the way open - so it's definitely due to the low voltage at the connection...it's confusing, though - how can that wire just suddenly have low voltage? It was fine earlier in the year...
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The choke needs high current flow to work correctly so there must be an issue someplace with the wiring and it is lacking "potential" to effectively supply the choke with enough current to work like it's supposed to.
That is a very easy problem to correct, you can run a new wire to it from a "keyed on" source. I like to go to the wiper motor as there is one wire there that works well for that purpose......Cliff
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It could be the oil pressure sending unit. There should be one above the oil filter. It allows current to the choke when there is oil pressure. Does the car have the choke/oil light? I had one fail once. Jumped it out.
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It does have the oil light on - coincidentally...that came on when the speedo cable detached, and all this started...I have oil on the dipstick (it doesn't leak any) and I'm pretty sure the engine would have seized by now if it actually had zero pressure...
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most likely the problem. You might have dis-connected it when messing with the speedo cable..
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That would explain a lot - it's pretty nice out, I'll give that a look at today.
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So my sending unit is up next to the distributor and the connection seems wayyyy looser than one would expect. It doesn't seem to snap down all the way, not sure how it would have done that on its own, but its 36 years old, so...I won't question it, haha.
I'm currently double checking that it is not intended to be that way, but it sure seems like that could be my culprit...
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I made a quick "jumper" cable (having bags full of crimp-on connectors is incredibly handy) to run between the terminals inside the connector and those on the oil pressure sender to ensure a good connection - fired the car up and right away, the oil light has gone away, and within a few minutes, the choke was totally open and the car was back to its normal self - and not smoking or trying to burn my eyes and nose with nearly-raw gasoline.
The old choke probably wasn't busted - but, I have a new one on there now, and the factory connector, so that is worth it to me (and I have the old one, just in case).
Now I just need to solve the other issue of that funky idle that'll hop up high (it was idling up to 2500 at first - really have to give it some hard revs to drop down to where it should sit. It's almost like a light switch when it changes to start running higher.
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It could be the oil pressure sending unit. There should be one above the oil filter. It allows current to the choke when there is oil pressure. Does the car have the choke/oil light? I had one fail once. Jumped it out.
Did not know this... That is some secret sauce.
There is some good info in this thread. The posts by Cliff on testing the Choke by grounding it, and how to set it up initially are great nuggets. Thanks Guys.
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glad to hear you got it figured out. Some of those models did have a very high fast idle, check the tune up label for fast idle spec. I guess they wanted to get the cat lit off as quickly as possible.