Here's the problem. When the engine is not running the throttle appears to close all the way. With the engine running it doesn't quite return to fully closed unless I let it snap close. Seems to hang up just slightly (1200-1500rpm)until I put a little thumb pressure on the linkage. Then it will drop down to 850. I put a stiffer spring on the linkage but it makes the gas peddle rather hard to push down. I just had the bushings replaced. Don't ya just love 37 year old carbs......

Check the choke side of the linkage.

Use some fine oil on the shaft. New bushings sometimes are a little tight. You can even use auto trans fluid. Work it back and forth. It should free up. If not, look for a 'rub' spot and hone it.

I will check both of those things. Is it the accelerator pump spring that actually closes the throttle. I'm also wondering if that spring isn't a little worn out

The throttle return spring closes the throttle. You really don't want too stiff a spring, as it pulls against the throttle arm and eventually causes wear on the shaft.

The accelerator pump spring has nothing to do with the throttle plates returning to closed. Binding anywhere in the linkage does.

The first time I reassembled a QJet after many years without touching one, I got the plastic choke cam/weight on the wrong side of the lever. It did just as you describe. I pulled the choke assembly back off, raised the cam, and put it back together. Take a look at those parts to be sure nothing is binding.

OK. Checked out all the linkage and new bushings. Absolutely no binding at all bewteen either of them. When the carb is on the car and the engine is off the throttle closes just fine. With the engine running the throttle will close if you let it snap shut. If you ease off the acelerator it will hang up. It's kinda like the engine vacuum is holding the butterfly valves open. Maybe my only option is a heavier throttle return spring, but this thing has got my couriosity up now so I probably won't be able to let it go.....Any thoughts................steve

Engine vacuum cannot hold the throttle plates open. Perhaps when your Quadrajet was reassembled one of the throttle plates was installed just enough off center to make it bind.

With the spring off, does it close smoothly by hand? Meaning that in that last area that won't close without the spring snapping it doesn't exibit a bind when closing by hand.

If it operates smoothly, you might want to try a stronger spring. You might be able to remove a loop or so from the spring and bend a new tang. The thing is that it's tempered steel, so cutting/rebending may create a weak spot where it's bent. I've seen it go both ways with what appear to be similar springs: One can be cut/bent without problems, another one will break when you bend a new tang, and yet another will fail sometime after cutting/bending.

I was thinking the same as Vikki about the throttle plates. When it was rebushed they had to be removed. Sometimes the tiny screws break off and the builder will have to drill and tap new threads. They can be slightly off center and bind. Look for a shiny spot where the plates might be rubbing.

I ran into the exact same thing recently and wondered if you ever figured it out? I am using essentially the stock return spring (repop) and my primaries close fine when the engine is off. When its running it won't close completely and when I pull to a light it will idle 1500-1800rpm (4spd). I rap the throttle and it drops down to 800-900ish. I checked it when I got home and it simply doesn't return to the stop when the engine is running? It doesn't appear to bind anywhere at all. Cliff Ruggles recently rebuilt the carb. I am sure a heavier spring would do it, but I too am now curious what the root cause is... I'll also take some of the suggestions off here and check them tomorrow.

Do you have an idle solenoid?

How can you tell that the primaries close fine when the engine is off?

Use a flashlight to look into the primary bores to be sure no gasket material is visible beneath the bores. Even a slight amount of interference will cause the plates to hang.