Quadrajet Help

[dgheinen]

My 68 has a 350 from a 72 truck, and a M4MC Quadrajet from a 1978 Chevy (Model unknown). The casting number of the Quadrajet is 17058204. My problem is this: the high idle circuit is not working properly, and I don't believe the choke is either. When I stab the throttle before starting the truck when it's cold, it doesn't kick it into high idle. I noticed the choke pull off diaphragm was bad, the pull off was very loose side to side & up and down, and the portion that moves in and out of the pull off (I am unsure what to call this) was bent. I replaced it with one from a Quadrajet I pulled off of my 78 C3 Vette, which had a working high idle and choke (before I went to an intake without provisions for a hot air choke). The choke plate also does not stay shut, and stays about 1/2 open. On the Quadrajet I have from the vette, when you move the throttle linkage all the way, it also moves the linkage on the passenger side for the choke plate/linkage, but on the truck nothing moves on the passenger side. What am I looking at here? I'm unfamiliar with how this choke system works. Any help is gratefully appreciated.

[geezer#99]

Take pics!
Likely something simple.

[dgheinen]

I'll see if this helps! With the truck off and dead cold, the choke plate looks like this


I replaced the choke pull off already. The one in this picture was from my Corvette's old Quadrajet. The arrow points to the lever/arm that moves with the throttle linkage on the Corvette Quadrajet, but not on the truck's.


Here is a bit better picture of the overall choke setup, in case someone sees something I'm missing.


Last but not least, here is a video just after shutting the truck off, so show what it is and isn't doing. The truck only ran for about a minute.
https://youtu.be/0aUzYWbRLhs

[geezer#99]

You need to loosen the three screws on the black cap and rotate the cap to the rich side. THere's a lean/rich arrow on the cap.
When you rotate it hold the throttle slightly open (I stick a little screwdriver into it) to hold it open.
As you rotate the cap the lever in your second pic should come up setting it on high idle and the linkage will close the choke blade.
THat top spring and screw is what you adjust to set how far open the choke blade is when you first start it. The lever will come up and touch it.
When you start it the motor creates vacuum, the choke pulloff compresses and the lever is pushed back down slightly so the choke blade opens enough to let it run.
There's a high idle screw down under the choke pull off. Hard to see but easy to adjust.

Hope all that is clear as mud!! LOL!!

[demian5]

You need someone to look it over who knows what they are doing.

From what you are saying, the carb was removed from another car, and the choke worked then. But the choke is obviously not working and need someone to diagnose why.

Do what geezer says till the choke plate closes and look at the line on the black plastic vs the lines in the choke housing. Then rotate to a neutral setting and try it out. It should be almost closed when dead cold, but not held closed, and the step on the cam should hold the throttle open as well.

The choke spring could be off of the lever inside of the housing.

You need someone to look it over who knows what they are doing.

[dgheinen]

Sorry if that was confusing! I have 2 Q Jets. The one on the truck, and a second one I pulled off of my Corvette. The Corvette Q Jet had a working choke when I pulled it off, so that's where the new choke pull off came from.

I loosened the three screws, rotated the black cap, and would you look at that! The choke plate closed. I set it so that it is almost closed, about 1/8" gap. It was dead cold this morning when I was playing with it, so I started it up, and it jumped to a super high idle. I backed off the high idle screw under the choke pull off to a steady RPM to let it warm up, and as the truck idled for a few minutes, I saw the choke plate open up and the idle drop. I bumped the throttle and it came all the way down to a steady low idle! So I believe it is now working just about the way it should be. I still may play with it a little bit, but overall I'm very pleased that I don't need to feather the gas for 5 minutes in the mornings anymore.

[geezer#99]

Use something to mark it on the cap in case you fiddle with it so you can set it back there if you need to.
I use whiteout (used for corrections on printed paper).

Good you got it working!

[demian5]

Glad you figured it out.