Alright, here are my tips for you, or anyone else that's reading this, to do this "fix" both with the carb on the engine, and with it off. Now remember, the goal here is to have your primary throttle blades set properly with regard to the transition slot, and your primary fuel/air mixture screws set properly so that your idle quality is nice at all under hood temperatures and so that your "light throttle" cruising has no lean surging. The idle RPM level will be set by the new secondary screw that you will be installing. The problem that you are trying to correct is that the density of the air that is going through the carb is WAY different when it is really, really hot as opposed to when in it nice and cool. Unfortunately, your carb only gets one single setting. Computer controlled fuel injection it ain't.
First, buy four 10-32 cap screws, a 3/4", a 1", a 1 1/4", and a 1 1/2". Then figure out which one of those four screws will be the most convenient to access with an Allen wrench once it is mounted to the same depth as the existing screw. Depending on your manifold and Turkey Pan combination, you might find that drilling an access hole in the Turkey Pan, that allows either a longer screw to poke through, or for the Allen wrench to come up through. Choose the screw that makes it easiest for you to get to, as you will be making slight idle adjustments once or twice a year, based mostly on the seasons. Inserting this screw can be done with the carb on the engine or off, but it is obviously easier to do with the carb off the engine. Insert your new screw with the same number of threads protruding up that the old screw had.
If you want to "get fancy," buy a 6 lb. spring, like you see in my pic above, and a washer for the screw. When you insert the new screw, just have the washer and spring "hanging loose" on it. Once the screw is adjusted properly, you can add that copper sleeve, that is just a piece of 3/8" copper tubing. It is cut to just the right length to apply good spring pressure. You get it around the cap screw by using your Dremel to cut a slot in the tubing so that it just barely slips on, and around the screw shaft, and then you use a pair of pliers to lightly squeeze the tubing tighter so it never falls off. That's how you get a perfect, custom fit. I also like to use a couple of drops of VC-3 "adjustable thread locker" on the threads. It doesn't harden, and allows you to make adjustments on the screw.
https://www.vibra-tite.com/products/...-3-threadmate/
If the carb is off the car, flip it over and adjust the primary butterflies so that there is a "square" or less of the transition slot exposed. If the carb is on the engine, and you don't want to pull it off, then back the idle screw off on the driver's side until you see a "visible opening" between the screw and the idle lever. Then, place a pencil, eraser side down, in to the primary side of your carb so the eraser is sitting on the butterfly valve. Put a sticky tab on the point end of the pencil. Then slowly tighten up the idle screw until you see the pencil and sticky tab start to move (meaning you are now opening the primaries). Give it another 1/4 or half turn, but no more. Now lightly seat both idle mixture screws and back them out 3/4 of a turn.
Start the car and adjust the idle level by turning your newly installed secondary screw. Once you have a decent idle, take the car for a nice gentle drive where you see how she cruises at, say, 40 MPH, with your foot just ever so slightly giving gas. You should experience "surging" because of the lean mixture. Back each idle mixture screw out 1/8 of a turn and do it again until you have a nice clean, even engine performance with no surging when she is cruising with your foot just lightly on the throttle.
If your idle is too high, back your new secondary screw out a bit, if it's too low, screw it in a bit. You may also turn your regular idle screw in a bit. BUT NOT MUCH -- remember, we don't want to go in to the transition slot. Less is more in that regard. If you have "ham hands" you can visually see how much you're adjusting the new secondary screw by placing a clothes pin with a stick attached to it on the driver's side secondary throttle shaft. As you tighten the secondary screw in, while standing on the passenger side of the car, you will see the stick move clockwise. When you loosen it, it will move counterclockwise. It doesn't take much of a turn to that new screw to make significant changes to your idle. For a big FE, with a Holley 4160 on it, and an engine compartment that gets pretty darn hot, this is absolutely the best way to get your carb set perfectly.
