1967 273 4bbl with Edelbrock 500 CFM Carb

The air screw adjustment should be adjusted as follows. Set the parking brake and chock the rear wheels. Start the engine and warm it up. Drop it in D once warm and get the idle speed "around" 650-700. Connect a vacuum gauge to a manifold vacuum port. I THINK that is the small port on the front of the carburetor, driver's side. Adjust each air screw to achieve the highest vacuum reading for each screw. Readjust the idle if necessary. Too many people get caught up thinking air screw adjustment should be X number of turns out, when in reality, the vacuum gauge is the way. I would run each screw ALL the way in and lightly seat them one at a time. If when that's done, the engine does not die or almost die, the carburetor is getting fuel form somewhere it's not supposed to and needs to be serviced. If it stumbles and or dies when each screw is turned all the way in, that's a good sign and go ahead and adjust as outlined. Good luck with it.

Also one more note......I agree that intake isn't the "best", but I don't believe that's the source of the problem. Also check the initial timing and let us know where that is.