Q-jet Air Valve tuning tip
The secondaries on Q-jet carbs have a secondary air valve spring that is adjustable which determines when the air door butterfly will open, allowing air to rush through the big secondary side of the carb. This has the obvious advantage of being tunable compared to some designs which aren't, such as AFB style carbs (which are great carbs for many other reasons). The problem is that changing the air valve spring setting is less than easy unless you have 3 hands and some time to kill. I found this simple tip in the November 2000 issue of Car Craft magazine that shows a way to make tuning/setting the air valve spring tension a breeze. The following text was taken directly from the magazine as printed, but I think there is a small error near the end. See my note following the text.
Adjusting secondary air-valve spring tension on a Quadrajet using a small screwdriver and inverted Allen wrench is no piece ot cake, especially in tight engine compartments. Fine tuning on your bracket car between rounds is even more of a drag. But there is some relief in sight; all that's needed is a length of 1/4-20 threaded rod (photo A, 1), a 1/4-20 wingnut (2), a 1/2 inch-id AN washer (AN96O-816, 3), a common commercial ¼-inch washer (4), and a spare Quadrajet accelerator pump spring(5). The as-delivered outer diameter of the 1/2-inch id AN washer is 1/8-inch (0.875). Grind it flat on two opposing sides (not around its entire circumference) to 0.760 inch (6).
Adjust the secondary air-door tension loose so the carburetor bogs. Screw the stud (photo B, 1) into the carb's air cleaner stud mounting hole, then drop the modified AN washer (6) into place over the stud so it seats atop the secondary metering rod hanger (7). Place the accelerator pump spring (5) in position over the rod against the modified AN washer, followed by the common washer (4) and wingnut(2). Tighten the wingnut by hand until the bog disappears; loosen the wingnut to bring the secondaries in slower. What could be easier? (And if you run an air cleaner, just use a longer stud and an extra wingnut.)
NOTE: From my understanding, loosening the wingnut would allow the secondaries to open sooner, not slower, as the article indicated. I haven't tried this yet, but I do intend to, and will update and/or correct things as needed.