Time to remember how to tune a 1920 1 bbl carburetor

I messed around with it some more today, made minor progress at best. I took the carburetor off and trimmed out the gasket around the one hole I thought might be an issue. Turns out it is the hole leading to the fuel vapor canister purge port. I screwed the one idle screw all the way in, felt it on the inside of the barrel, then turned it back out 2 turns.

After getting the engine running, I spent some time checking for vacuum leaks. I blocked off the tiny EGR vacuum port, which didn't change anything, then used Vise-Grips to pinch the vacuum reservoir line shut. No difference there either.

I did get it to idle a little lower, maybe 1200-1300 rpms or so, vacuum gauge showed around 15, but still the same issue, turn the throttle stop screw down another 1/4 turn and it dies. I tried changing the idle screw from 2 to 2-1/2 turns out, didn't make a noticeable difference there either.

That flapper valve in the exhaust manifold seems to work, it spun freely, but the spring was broken, so it did not snap to one direction or the other. I tried with it turned all the way one way then the other, no difference.

The one modification I had planned for the car was a Super Six Carter BBD setup, maybe I should just switch it over if I can find all the parts in one spot. Aluminum intake, throttle cable bracket, kickdown linkage, a Carter BBD carburetor and air cleaner, etc.