Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: TravisUT on October 07, 2024, 06:11:32 AM
-
Hello, new member here; Apologies if this is a duplicate post! I'm having some issues with my carb and was wondering if anyone could help.
I have a Quadrajet 4 barrel (17080212-1024), mounted to a stock intake on an 84 C20 454. I recently replaced the hot-air choke with an electric choke, and since then, almost every time I start the truck, I get wet black spatter shooting from the exhaust pipe, along with some fuel-smelling smoke. Once the engine warms (choke opens very quickly), the smoke clears and the truck runs great. With the hot-air choke, this problem didn't happen. Also, I recently replaced the spark plugs (they were all fouled, very carbon coated). I don't know if the fouling was just since the electric choke was put on, or if it's been running rich for the last 3 years (since engine and carb rebuild). I've tried adjusting the air/fuel mixture screws, based on RPM, but that didn't seem to help much.
Should I go back to the hot-air choke, or what can be done? I'm not a mechanic, but am comfortable with working on the equipment.
-
Sounds like the pull off isn't opening the choke on start up. It should open about a 1/4 inch on start up.
-
Some items to consider... The hot air choke had some built-in idle air bypass by design.
You may not have that going on now with the electric choke. Did you change the choke housing
or just the bimetalic coil/cover? Do away with the hot air tubing?
Make sure the loop in the bimetalic coil engages properly with the peg inside the choke housing.
Crack open the throttle and make sure you can twist the black cover and move the choke both directions. Dont reuse the housing gasket and source the choke power from key-on.
That carb should have a rear and front pull-off. The front pull-off also controls the secondary
air valve. Never been a fan of any of the rear pull-offs.I would remove it for now and just
use the front pull-off. Make sure it cracks the choke about a 1/4 inch as 77 mentioned.
QJ
-
I just changed out the coil/cover, and did away with the hot air tubing. I still have them though. I will be checking the pull-off's today! In regards to tuning/adjustments: what is the best order to make the adjustments? Should I do the fast idle, primary pull off, secondary pull off, and then choke adjustment, in that order? Or a different order? I'm worried that one adjustment will mess up the other...
-
I assume the pull-offs tested good....?
Prop the throttle open a little bit so it doesnt interfere, Rotate the choke cover back and forth
to make sure theres no binding,turn it til it just closes and tighten it down. Apply vacuum
to the front pull-off and it should barely crack open. Note that you can push it a little
more open with your finger due to the normal slop in the link. This is where you want the 1/4 inch
gap mentioned before. there is a spring loaded phillips screw on the pull-off to adjust this.
When you crank it up you will have to work quickly back and forth with the speed screws
and it will take several cold start cycles to get it dialed in.
QJ
-
I was waiting for a hand vacuum pump from Amazon, and of course the 2-day shipping turned into 3-day, so it won’t be here until tomorrow. >:(
If I understand correctly, when applying the vacuum to the pull of, I want it to just crack open; and when pushing the pull off linkage all the way in, the full gap should be 1/4”…right?
-
I should have been more clearer, you will fully retract the pull-off which should slightly crack the choke blade open then push lightly on the CHOKE BLADE for the 1/4 in. gap betwix the top of the choke blade and the air horn. adjust with the phillips screw on the pull-off.
You can do this with mouth vacuum and a piece of hose. doesnt take much.
-
This may help some.
Measurement is usually around .160"-.180" at upper/rear end of choke blade for M4 Qjets.
-
Ok...I think it's all adjusted now. Got the choke and pull off's set, and it seems to be running good. Didn't spit any wet black spatter, so that's a step in the right direction. Once it was running, I hooked a vacuum gauge up to the big manifold port on the front-bottom of the carb, and adjusted the idle mixture screws to vacuum. Both are set about 3 turns out, and I'm getting 18 inches of vacuum. Is that good/ok?
I'm still getting a bit of smoke, but only on revving; idle and drive is ok with no smoke. I pulled a plug and it was all black. I just replaced those plugs a couple of weeks ago, but I suspect the out-of-tune was causing issues, yes? I don't want to replace them until we're confident the underlying cause is fixed...thoughts?
-
Nows the time to set/check all aspects of ignition timing, then get it out on the road
and put some miles on it. That may burn off some plug fouling.
18 inchs of vacuum is probably good. @ what rpm? Ported or manifold vacuum?
HEI distributor?
You may still have some cold start tuning to do but sounds like its close.
QJ
-
HEI ignition, idle RPM is around 700-720 with choke off, tested using manifold vacuum. My timing at idle is showing about 1" in front of the timing tab, which ends at 16... Vacuum advance is hooked up as well.
-
"I hooked a vacuum gauge up to the big manifold port on the front-bottom of the carb."
Here is where the hose from the PCV valve should be attached and since it´s a calibrated "vacuum leak" it should be attached while adjusting the idle needles.
Also, timing is to be adjusted with the ignition vacuum advance disconnected and plugged.
Does your carb have a new float and inlet valve?
-
Thanks @Kenth.
If the PCV valve should be attached while adjusting, where do I hook the vacuum gauge up to?
Yes, carb has all new parts.
-
I would use the port right above the fuel inlet for the vacuum gauge.
-
"I just changed out the coil/cover, and did away with the hot air tubing."
You MUST block the vacuum supply to the choke housing to do an electric choke "conversion". You will loose any idle bypass air if the carb was drilled for it.
If you don't block the vacuum supply then you have an unfiltered vacuum leak plus you are drawing air into the housing to cools the electric choke coil......
-
Yes, I have blocked off the hot-air intake ports.
-
Carb seems to be running good, from what I can tell with my limited knowledge. Truck starts right up and drives just fine. However, still getting some wet spatter dripping from the exhaust pipe during warm up. My idle mixture screws are 3.5 turns out, set with vacuum. Do they need to come out more? How long should it take to burn the richness out now that the carb is adjusted? I just don't trust it...
-
I don't understand "blocking the hot air intake ports". Did you block them at the housing or BEFORE the housing?
-
Blocked off at the housing. I've included some pics and video of what's happening. Started it up this morning and got very little, if any, smoke, but still the wet spatter. In touching & smelling it, I think it just water, doesn't smell like fuel. However, the exhaust smell is very "rich", burns my nostrils when smelling it. When starting it, the truck starts right up, and the choke will open very quickly, within just 2-3 mins, and the rpms will skyrocket until acceleration when the cam drops.
Also, I just noticed today that the airhorn gasket is wet with fuel, around the accelerator pump at least.
Here is a link to the videos: https://photos.app.goo.gl/67hDm1C7zcf3LjRf8
-
Part of the electric choke "conversion" requires blocking off the vacuum supply BEFORE the housing. This can be done under the plastic choke seal, inside the plastic choke seal, or in the passage in the housing just after the seal.
Otherwise you have not only a vacuum leak that sucks unfiltered air into engine, it pulls in cold air that can effect the operation of the electric choke.
You mentioned that the engine and carb were "rebuilt" 3 years ago? What exactly was done to the engine? Did you put one of my rebuild kits in the carburetor?
Running rich ever since this work indicates something isn't quite right someplace and may be contributing to your issues......
-
Thanks Cliff. Do you have some pictures of those locations, to help me understand better?
Engine had a cylinder that was stuck with rust; had an engine shop strip it and rebuild it. Carb was disassembled, cleaned and rebuilt, using a kit from another seller.
-
Since your problems have been present since the "rebuild" I'd get one of my rebuild kits and start over. While you are in there check the power piston height, and make sure the power piston hanger arms aren't bent, up, down, or both. Since you used someone else's kit that may be part of the root issues you are having, low quality/incorrect internals, gaskets, etc. My rebuild kits are application specific and not "generic". They come with the correct parts, and highest quality in this industry. They are also the most complete in this industry......