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Quadrajet Advice Wanted
#775195 April 27th 2021 1:33 pm
Joined: Apr 2021
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Akinak Offline OP
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Long story short - I took my van (85 vandura 305 quadrajet 4bbl) to a mechanic to replace the intake manifold gasket. When I got it back he said “your carb needs to be rebuilt, floats are sticking and choke doesn’t open. And your fuel air mixture was turned out 3 1/2 turns, normal is 1 1/2”. So he adjusted my carb and it ran like sh*t. However it ran just fine before. I got the van back and started reading. I bought a vacuum gage and a carb adjustment tool with the double D end. I adjusted the air/fuel to max vacuum and turned the choke so that it was barely cracked open at cold. It runs great after warming up now. However it idles high even after a warm up until I take it for a drive, then it settles down. Thoughts on what could be the issue?

Re: Quadrajet Advice Wanted
Akinak #775203 April 27th 2021 4:41 pm
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Rust N Dents
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I do have one piece of advice...
Don't ever go back to a mechanic that makes your vehicle run worse than when you took it in.

On your current issue...
How long do you have to drive it before it calms down?
Normally, you'd just tap the gas to free the choke lever, then the idle would settle down, right?
Your "mechanic" mentioned the choke wasn't opening...
Maybe it's sticking?
It could be gummed up a little... just enough that it only has time to open all the way when you've been pressing the gas for a little while.
That's the only thing I can think of off-hand.


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Re: Quadrajet Advice Wanted
Akinak #775215 April 27th 2021 8:21 pm
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Yep, Rusty sounds dead on. I'd suggest rebuilding or getting it rebuilt though. Doesn't take long for one to gum up and get full of varnish from sitting and poor quality fuels. They're not hard to rebuild at all, and are a fine carburetor. I prefer Holley, but I've run QJets for many years.

In the mechanic's defense, he can't do much in the way of fixing the problem without rebuilding the carb, BUT he really shouldn't have adjusted anything without asking first and at least letting you know it might make the issues worse. You did the right thing by grabbing that vacuum gauge and getting it close.

Grab a carb kit, some new floats (I never put the old floats back in just for piece of mind), and a few muffin pans. Use the muffin pans to store the hardware as you remove it, helps keep things in order as well.


[Linked Image from live.staticflickr.com]

Re: Quadrajet Advice Wanted
Akinak #775256 April 28th 2021 6:02 pm
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My question is, how likely is it that the electric choke warmer is bad? And is there a tried and true way to determine that?

Also there is a length of silver duct that goes into the air intake snorkel from the exhaust manifold that is broken, is that something that can contribute to this issue?

Re: Quadrajet Advice Wanted
Akinak #775258 April 28th 2021 6:06 pm
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carpal tunnel
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If you're backing the idle mixture out more than two turns you could have a fuel leak. The Quads are known to leak internally between the body and the valve plate. I've epoxy'd up a hundred of 'em back in the day. If so, then some of that fuel could seep into the manifold while it's running due to manifold vacuum. That could require backing out the air adjustment to compensate. The 80's were not as bad as the 60's/70's but they didn't run as well either.
Sometimes, if they leak a little after shut off, you can have a wet or flooded start that can imitate a sticking choke.

As for the fast idle, check your choke pull-off diaphram (if equipped) and choke linkage. Previous owners/mechanics may have bend the linkage trying to jury rig a fix. The choke, if it's engaged, will block the rear air valves from opening. If the back barrels will open then the choke is open. But if you still have a fast idle then it's likely a linkage problem.

Rebuilds are easy and cheap.

Re: Quadrajet Advice Wanted
Akinak #775259 April 28th 2021 6:14 pm
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carpal tunnel
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Jump power to the choke to check it. Shouldn't take but a few seconds to tell.
The silver duct routes warm air to the carb from around the exhaust manifold during cold starts. There should be a valve in the snorkel that senses the air temp and closes that off after warm up. Not necessary but would help with cold start driving during the winter's up there.

Last edited by CatFish; April 28th 2021 6:15 pm.
Re: Quadrajet Advice Wanted
Akinak #775262 April 28th 2021 7:06 pm
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Yep, everything CatFish said is dead on too bud.

I've heard a few people say they've had good results when dealing with this company. They were intent on having the Qjet rebuilt for factory correct muscle car restorations. Just in case you don't feel comfortable rebuilding it yourself.

Quadrajet Rebuild Service

I've rebuilt about 20 or 30 in my day, but that 25-30 years ago. The last one I did was on my 72 Chevelle in 1998 and I ran that one for about 1 year and found a smoking deal on a good Holley 600. I could tune the Holley much easier at the drag strip, so I never went back. I've still got a few Qjets in my big carb basket on the parts shelf, but they're just sitting there collecting dust.

With a stock 305 though, you're going to be better off sticking with a stock Qjet or one of the small CFM Holleys. Holley recommends 390-465 CFM for a stock 305, which are $540-$620 depending on which you go with. I've got a 600 Holley I'm going to try on my 305, but I have a feeling it's going to run way too rich and I will be rebuilding one of my old Qjets for it.

Holley Carbs


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Re: Quadrajet Advice Wanted
Akinak #776796 May 27th 2021 3:49 pm
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The later quadrajets with the metric idle speed screws came from the factory 5+ turns out. If it is only 1.5 turns out it is barely unseated and the idle mixture holes are already tiny. Put a vacuum gauge on it and open them up.

I created this series of posts on the Quadrajet I built for my 383 to run on the stand.

I had to cut the caps off and they were 6.5 turns out on this 84 carb from GM.

With the idle down tubes, idle channel restrictions and the idle mixture screw holes all opened up I started at 4 turns out on the bench. When I got it running on the 383 I ended up having to open them up another 1.5 turns. I have seen an 80 L82 350 Vette carb that was 8 turns out factory.

https://www.thirdgen.org/forums/carburetors/775566-850cfm-m4me-q-jet.html

Last edited by 1983G20Van; May 27th 2021 3:54 pm.

1983 G20 Conversion Van, 350 TPI, Reed Hydraulic Roller cam, Ported 906 Vortec, Edelbrock 3817 TPI-Vortec Base, Doug Thorley Tri-Ys, Dual 2 1/2" exhaust, Speed Density 7730 ECM tuned by ME, 700r4 by ME, Stock 1,600 rpm converter, Rebuilt Stock 10 bolt with posi by ME, 3.08 gears, 358 RWHP @ 5,200, 384 RWTQ @ 3,400, 14.66 @ 95.43 w 2.28s 60'

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