I have a couple of questions about a Quadrajet with an electric choke:

(1) There is an adjustment screw above the electric choke housing on the Quadrajet I put on a 455. This screw has a captive spring around it and the tang on it drops down into the choke mechanism. What exactly does the screw do as far as the choke operation goes?

(2) The "climatic control" on this carb has had the rivets removed and screws installed so you can adjust it. which way do you rotate it to shorten the amount of time the choke stays on?

Thanks in advance for any help. I'm a Quadrajet "novice" and although I like the carb so far, I would like to know more about how the choke system works. I have ordered the book from Cliff Ruggles, but its not here yet. This carb is from SMI, and the instructions don't have much information about the choke at all. I could probably call SMI and have him tell me how these two adjustments effect the choke...but I thought I would ask on here and see if some of the Quadrajet fans on this site could help me out in understanding this carb.

 

(1) that is the vacuum break adjustment screw, it sets how far the choke valve opens after the engine starts while the choke is on. if your carb. has two vacuum break units, this would be the primary vacuum break adjustment.

(2) rotating the choke cap clockwise reduces the amount of time the choke is on, counter-clockwise increases it. this corresponds with the rich/lean setting that is possibly marked into the choke cap.


bill

 

Thanks for the reply Bill. OK, this carb just has just the one vacuum break unit. So this "vacuum break adjustment screw" is what sets how far the choke valve remains open when the car is started (and its cold enough for the choke to be involved).

I have been watching the choke operation and I see how when there is 12V applied to the choke coil and you operate the throttle, the choke valve snaps all the way closed. Then once the car starts, the vacuum pull off opens the choke valve just a little bit. So you are saying that the vacuum break adjustment screw is what is used to change how far the choke valve is open at this time. Its obvious that would have an effect on the A/F ratio for while the choke is on. Is there a way to figure out how far that valve should be open for a not-to-rich/not-to-lean choke condition? How about a standard setting to start from?

I rotated the choke cap clockwise and it did the trick as far as letting the choke come off sooner and getting it down off high idle sooner. There are two spots on the fast idle cam, one takes it to 1400-1500 RPM when I first start up. What determines when the choke system will allow you to kick it down to the lower step of around 1100-1200 RPM? Is that lower RPM still related to the temperature of the choke coil and the tension its applying to the choke valve?

I'm real close to getting the choke dialed in, but you only get a couple of trys and then its not a cold start any more.

I did the idle mixture adjustment once at operating temp, and got to 15" of vacuum in park at 850-900 RPM. It drops to 12" idling in gear at 700 RPM with the brakes on. These values are higher than what I was getting with the previous 4150 style Holley.

After this its on to a bog/hesitation when I floor it. The motor seems absolutley lost for a couple seconds and then takes off when you back out of it a little. Just driving around "normal" feels smooth and powerful, but if you try to tromp on it, it bogs real bad and sometimes theres a backfire. I believe the next adjustment will be the "secondary air door tension". What are other things to look at when trying to get rid of the dreaded "Quadra-Bog"?

 

I usuall set the air door with little tension, without a problem!
Once bought a rebuilt, put it on @ the auto parts store, and when I took it around the block, got the same problem - bog and backfire!
Checked it out, and found the cam that lifts the rear metering rods was broke!
Since I waited a week for a 'special order' carb, I took the cam off my original carb, ['69 442 auto/air] and replaced it on the new one - worked great!
Never saw another broken one!
With the car off, open the secondaries manually, and see if the air door lifts the metering rods when you open it.