WEIRD Quadrajet Throttle Issues?

[savatreatabvr]

Just bought a remanufactured Quadrajet off Craigslist. My issue is after bolting it on the RPMs raced up to 3000 rpms just like it would if I forgot to hook up the throttle return springs but the springs were on and the throttle was in the normal idle position but it definitely didn't idle, lol! So I backed out the idle speed screw all the way and started it again, same thing but only 2000 rpms this time. Thinking I had linkage binding up I installed a thick gasket (pics below) between the manifold and Quad to raise it up off the manifold but the gasket has 4 hard plastic pieces that the bolts fit through. I'm wondering how the gasket can seal properly with hard plastic pieces flush with the gasket surface? Anyways the racing RPMs issue is still there so could I have something internally wrong with the Quad, like stuck metering rods or stuck power piston?

[4x4k30]

it sounds like you do have a stuck metering rod i would check the secondary rods first they are the ones on the top and with the biggest air flaps if they are stuck open it will draw vacum and idle high also it could be a piece of thrash these carbs are bad about acting up if they have set up for a while,, also the gasket with them plactic inserts will seal up ok because really the carb base gasket covers the base around the carb and intake the plastic inserts are just so you wont over torque the carb mounting bolts

[savatreatabvr]

Originally Posted by 4x4k30

it sounds like you do have a stuck metering rod i would check the secondary rods first they are the ones on the top and with the biggest air flaps if they are stuck open it will draw vacum and idle high also it could be a piece of thrash these carbs are bad about acting up if they have set up for a while,, also the gasket with them plactic inserts will seal up ok because really the carb base gasket covers the base around the carb and intake the plastic inserts are just so you wont over torque the carb mounting bolts

So I need 2 more gaskets to sandwich the thick gasket with the plastic inserts?

[4x4k30]

Originally Posted by savatreatabvr

So I need 2 more gaskets to sandwich the thick gasket with the plastic inserts?

no you should just use the one thick gasket with the plactic inserts.if you try to stackem they will suck air. i just replaced my carb base gasket the other day its just like the one in your pic .

[savatreatabvr]

Since I don't have a EGR valve, factory air cleaner or vacuum canister do I just plug the vacuum ports on the Quad and I'm trying to find a decent vacuum diagram online but the problem is there are 50,000 different diagrams! Where do I find a good diagram?

[4x4k30]

what did the gasket look like that you first took off?

[geezer#99]

Did you check the high idle screw. It's under the choke pull off.
What year of truck?

[4x4k30]

Originally Posted by savatreatabvr

Since I don't have a EGR valve, factory air cleaner or vacuum canister do I just plug the vacuum ports on the Quad and I'm trying to find a decent vacuum diagram online but the problem is there are 50,000 different diagrams! Where do I find a good diagram?

what vehicle do you have ? also when you swaped carbs did you have all the vacum lines pluged on the carb? there are 2 big vacum ports one on the back and one in the front if they were left open it will make it idle real high.

[savatreatabvr]

It's a 73 Chevy c20 454, I had a squarebore Edelbrock 1407 on it so I used the Edelbrock adapter. Since the Quadrajet is a spreadbore i don't need the adapter so the gaskets don't matter. The 1407 only had 4 vacuum lines, the PCV, the brake booster, ported vacuum and full vacuum. The Quadrajet has like 6 vacuum ports, 3 of them are big and finding a good vacuum diagram is quite difficult. I pulled the choke off because it is a hot air choke and I didn't have the lines from the manifold to choke and there is a small hole (red arrow in pic below) where the choke fit into a plastic piece that I plugged thinking it may be a vacuum leak. Could plugging that be an issue?

[superwade57]

There's a big port in front center for pcv a bigish one rear center for tranny smaller one up front for vacuum advance on dizzy if your brake booster is pulling vacuum off carb it'll be a big one bottom rear center

[4x4k30]

Originally Posted by savatreatabvr

It's a 73 Chevy c20 454, I had a squarebore Edelbrock 1407 on it so I used the Edelbrock adapter. Since the Quadrajet is a spreadbore i don't need the adapter so the gaskets don't matter. The 1407 only had 4 vacuum lines, the PCV, the brake booster, ported vacuum and full vacuum. The Quadrajet has like 6 vacuum ports, 3 of them are big and finding a good vacuum diagram is quite difficult. I pulled the choke off because it is a hot air choke and I didn't have the lines from the manifold to choke and there is a small hole (red arrow in pic below) where the choke fit into a plastic piece that I plugged thinking it may be a vacuum leak. Could plugging that be an issue?
no that shouldnt be a problem plugging that one also you should plug all the ones where you took off the choke and that little piece you left on there is the lockout for the secondaies it needs to come off it will hang and cause the secondaries to hang open or closed .i would just use the ports you need like the pcv its the biggest one port on the front . the one in the back for the power brakes and find one with full time vacum for the dist. advance and just plug off the others you dont need..also some qjets have a big port on the top rite above the fuel filter inlet its just a vent for the carb it should run to a charcol cannister if not just plug it off .hope this helps

4x4k20

[savatreatabvr]

Originally Posted by 4x4k30

4x4k20

I've plugged everything I don't need and when I start it now it's like stating it with my foot to the floor! No kidding, the RPms race up to 4000 rpms with the throttle in the idle position and the return springs tight! Would the metering rods, the power piston or check ball being stuck or not present cause this problem? As far as I know whomever rebuilt the Quad could have left out a few parts or bent the metering rods or something. I guess I'll get a kit, pull off the Quad and see what's going on internally. The guy I bought it from just may be getting an early Xmas gift right through his front living room window, lol!

[savatreatabvr]

Originally Posted by geezer#99

Did you check the high idle screw. It's under the choke pull off.
What year of truck?

I'll check the high idle screw today, if it's that simple I'll kick my own a-s for being a moron for not checking that first!

[cadillac_al]

Make sure the secondary linkage isn't hanging up. I have it happen once in a while if a vehicle sits a long time. Shouldn't really happen on a new rebuild but something could be a little bent or something. As said before, move the secondary air flap and watch the needle hanger move up and down to make sure that isn't hanging up. It sounds like all extra vacuum holes are plugged. good luck.

[geezer#99]

Originally Posted by savatreatabvr

I'll check the high idle screw today, if it's that simple I'll kick my own a-s for being a moron for not checking that first!

Having looked at your pics, the high idle screw won't change anything. You've shot yourself in the foot by removing the choke system. Your high idle is caused by the secondary lockout tang being jammed onto the secondary throttle pin holding the secondary throttle open.
Look in this link at the diagram to see what the lockout and pin should look like.
http://67-72chevytrucks.com/vboard/s...d.php?t=605407

If you turn your arrow around in the pic it'll point right at it.
FWIW you can adapt an electric choke to the hot air style by changing the black cap.

[ironroad9c1]

yea metering rods won't do anything about idle speed, the butterflys have to be cracked open for you to get a high idle.

[motornut]

when those type of chokes act up I just tie it off, then you rule it out
not sure how long yours would be on? in AZ?

[savatreatabvr]

Originally Posted by geezer#99

Having looked at your pics, the high idle screw won't change anything. You've shot yourself in the foot by removing the choke system. Your high idle is caused by the secondary lockout tang being jammed onto the secondary throttle pin holding the secondary throttle open.
Look in this link at the diagram to see what the lockout and pin should look like.
http://67-72chevytrucks.com/vboard/s...d.php?t=605407

If you turn your arrow around in the pic it'll point right at it.
FWIW you can adapt an electric choke to the hot air style by changing the black cap.

No that's not it. I found the problem, the hanger on the power piston that the metering rods hand from was bent to the passenger side so one metering rod was seated and the other was raised. I bent it back and it cured the racing RPMs issue. Now it's not wanting to idle, I contacted the seller and he said he'd give my money back, yeah we'll wait and see what happens with that!

[83GMCK2500]

Clarify "not wanting to idle." In trying to lower the racing idle did you back out the idle screw too much, or further than is now needed with the metering rods corrected?

[savatreatabvr]

Originally Posted by 83GMCK2500

Clarify "not wanting to idle." In trying to lower the racing idle did you back out the idle screw too much, or further than is now needed with the metering rods corrected?

That's the thing, how far is the screw supposed to be in, in the first place? I can screw it in to make it idle but it idles high and poorly. It's kinda acting like a major vacuum leak but I don't hear it or found it. It wants to rev up fine but still have to feather the throttle to keep it running. I did decode the carb and found out that the top plate is for 1971 Oldsmobile, the body of the carb is for a 1978 Chevy Calif model and the bottom plate is from a 1978 Buick. Can mixing these parts together cause my problems? I guess finding a numbers matching Quadrajet now a days is probably pretty hard?

[83GMCK2500]

I've recently been tweaking and fiddling with mine a lot. Where are all of the numbers on a quad and where did you decode them? I know where the main set of numbers are on the driver's side of the body stamped vertically are, not the others.

For reference this is the idle screw I am talking about:


I might be able to snap a pic of mine, currently adjusted to a ~750RPM warm/hot idle.

[savatreatabvr]

Originally Posted by 83GMCK2500

I've recently been tweaking and fiddling with mine a lot. Where are all of the numbers on a quad and where did you decode them? I know where the main set of numbers are on the driver's side of the body stamped vertically are, not the others.

For reference this is the idle screw I am talking about:


I might be able to snap a pic of mine, currently adjusted to a ~750RPM warm/hot idle.

The top plate numbers are not stamped, they are in a circle and raised on the front passenger side and the bottom plate numbers are the same but in the rear drivers side. Here's the link to decode your Quad:

http://quadrajetparts.com/decode-you...retor-t-5.html

[savatreatabvr]

I just can't win! I took back the Craigslist Quadrajet and the guy exchanged it with another 800cfm Quadrajet, I was just as impressed with the 2nd one as I was with the 1st one because it also was nice and clean and looked factory fresh (pic below) but just like the first one the 2nd one does not idle worth a SH-T! That brings me back to the base gasket and those hard plastic inserts at all 4 corners, they are just as thick as the gasket is so how can the gasket create a good seal if it can't compress? No seal means major vacuum leaks! The gasket needs to compress right, or am I wrong? THIS COULD BE A CASE OF BUYER BEWARE OR A CASE OF GASKET STUPIDITY ON MY PART?

[cadillac_al]

Is this a new gasket? Normally those plastic inserts aren't an issue and they actually protect from over-tightening and warping the carb. So, you got 2 rebuilt carbs and they both idle too high? It must be something else but the only thing it could be is a massive vacuum leak. Does the carb set pretty even on the gasket with no rocking?

When I bought a rebuilt carb off ebay it ran perfect when i put it on the car and didn't even have to adjust the idle. Some guys do know how to set them up perfectly on the bench. It's strange that you are having such a problem with your carb since the guy you got it from apparently sells carbs regularly..

[savatreatabvr]

Originally Posted by cadillac_al

Is this a new gasket? Normally those plastic inserts aren't an issue and they actually protect from over-tightening and warping the carb. So, you got 2 rebuilt carbs and they both idle too high? It must be something else but the only thing it could be is a massive vacuum leak. Does the carb set pretty even on the gasket with no rocking?

When I bought a rebuilt carb off ebay it ran perfect when i put it on the car and didn't even have to adjust the idle. Some guys do know how to set them up perfectly on the bench. It's strange that you are having such a problem with your carb since the guy you got it from apparently sells carbs regularly..

That's why I'm thinking the base gasket is not sealing correctly because of those plastic inserts. The Quad is acting like it has a massive air leak and not sure where else it could be coming from. It's not idling high now is running rough and the exhaust seems to be louder for some reason, I guess that could be timing?