Quadrajet Choke and Fast Idle Linkages

[MaverickH1]

I just rebuilt my '82 K20 Suburban carb and the fast idle doesn't appear to be working. I tried to start the truck in the cold weather by pushing the throttle to the floor and then slowly releasing it, then cranking. But it just cranks and cranks. I have to pump the gas while cranking to get it to start.

Then I have to hold the gas down slightly to hold it at slightly higher RPMs for a few minutes while it warms up.

Something doesn't feel quite right to me about the whole fast idle cam/choke levers/vacuum breaks. I've tried looking at the GM service manual I have and it doesn't even have my carb set-up in it. All the videos I've found online don't seem to have my carb set-up either. I don't know if I have some "rare" HD emissions hybrid hot air choke with cruise control and A/C... or what. For example, this is a picture I took when I first took the carb off the truck in an attempt to remember how it all goes back together:

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One thing that sticks out to me is how the Front Vacuum Break doesn't even have a linkage to the linkage block on the upper left of the carb in this picture. In practically every carb I see online that Front Vacuum Break connects directly to that block, but in this case one of the linkages from the Rear Vacuum Break is there instead. Additionally, there's another linkage that goes from the Rear Vacuum Block and connects somewhere under the choke.

The fast idle and levers in this area kind of just flail around. I expected them to be... sprung by something. Is there a way to put those linkages back together and they be on wrong? Maybe they spring into action if there's vacuum on the Rear Vacuum Break? I went very slowly through the rebuild and replaced everything as it came out... so I thought.

The carb # is 17080213. I purchased a new Rear Vacuum Break (Standard Motor Products CPA306) but the thing has only one spot for rods/linkages to go even though it's supposed to fit my carb #. CPA337 looks more like the one that came off the truck, but Summit and RockAuto both say that fits a different carb number. I already replaced the front one since I'm trying to replace every critical rubber component as I do this rebuild.

Extra pictures I took fresh off the truck before the rebuild:

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And then a picture of how it is currently:

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[fast 99]

Hard to say if assembled wrong in those pictures. Make sure choke plate closes when cold. Usually, the index mark is somewhere near the housing adjustment marks. Some thermostats are keyed and cannot be adjusted.

The primary [front] pulloff will usually need adjusting. Apply vacuum to it, choke plate should open slightly, may be enough to get a 3/16th drill in the rear between upper housing and plate. Open the throttle plate for testing.

Make sure the fast idle cam moves freely and none of the linkage is bound up.

Did you replace the seal in choke housing? It's under the weight inside. If not it may drag on shaft and stick choke operation.

 

[75gmck25]

I also have a1708213 Quadrajet. Here is a picture of the pull-off and choke linkage.

 

[mtbadbob]

The front pull off should somehow be in contact with the green lever, at the end of the adjustment screw I think? This should open the choke as the engine warms & pulls vacuum. The AJ tab is just a weight to release the choke with the blip of the throttle when engine warms. It's been a while since I've done a kit too, so my memory isn't as sharpened as it once was. One thing I always do with that choke is bench set it so that the horn is slightly open, 1/16th-1/8, otherwise it'll load up at first start up. I then adjust if needed when engine is running and still cold, so it idles smoothly.

 

[MaverickH1]

I also have a1708213 Quadrajet. Here is a picture of the pull-off and choke linkage.

Thank you for the picture! What is the front pull-off contacting in that picture? Mine isn't touching anything at any point.

Looks like your rear vacuum break is brand new. Do you have a part number for that? The replacement one I got from RockAuto only has one location for the linkage, not the two locations like yours and my original one did. But I don't know internally what is different between all of them. Have you confirmed that yours works?

 

[MaverickH1]

Hard to say if assembled wrong in those pictures. Make sure choke plate closes when cold. Usually, the index mark is somewhere near the housing adjustment marks. Some thermostats are keyed and cannot be adjusted.

The primary [front] pulloff will usually need adjusting. Apply vacuum to it, choke plate should open slightly, may be enough to get a 3/16th drill in the rear between upper housing and plate. Open the throttle plate for testing.

Make sure the fast idle cam moves freely and none of the linkage is bound up.

Did you replace the seal in choke housing? It's under the weight inside. If not it may drag on shaft and stick choke operation.

I'll check more of this when I work on it some more, hopefully tomorrow. But it's hard to know when I'll get time. I really need to figure out the driveline vibration as the most critical thing first.

It doesn't feel like anything pulls those fast idle cams upwards at any point. Everything kind of just flops around and doesn't feel connected to anything.

Even the front choke pull-off doesn't seem to touch anything. Doesn't seem like adjusting anything will work, but maybe I need to bend the plate on it so it does, I'm not sure. Or... has been mentioned before... maybe RockAuto part numbers are wrong for this type of carb and I got the wrong one?

A lot of things to be unsure about. I'm used to "buy a part and slap it on and it works" type vehicles. Not ones where you bend linkages for adjustments and pulling off a factory original part could look completely different than the "right part" that replaces it.

 

[MaverickH1]

The front pull off should somehow be in contact with the green lever, at the end of the adjustment screw I think? This should open the choke as the engine warms & pulls vacuum. The AJ tab is just a weight to release the choke with the blip of the throttle when engine warms. It's been a while since I've done a kit too, so my memory isn't as sharpened as it once was. One thing I always do with that choke is bench set it so that the horn is slightly open, 1/16th-1/8, otherwise it'll load up at first start up. I then adjust if needed when engine is running and still cold, so it idles smoothly.

Nice, thank you! I'll try some of this hopefully tomorrow if I have time. Right now all of the green lever and the AJ tab and everything there just drops down fully clockwise and never raises up. With the engine off if I give it some "throttle" it will unlock and come up all the way if I'm pulling it up manually, but just drops down like nothing is really holding it.

 

[MaverickH1]

I took way too long to update this!

So my choke wasn't rotated the correct way, hence why the levers and such were just flopping all over the place with no tension on them. I rotated the choke to the original position from my pictures and everything immediately worked semi-properly. I suspect a lot of things still need adjustment, but it at least engages the fast idle circuit and the choke is working as it should.