383 stalls out during throttle transition - >?

I am having a problem with my 383 that's been getting progressively worse, now the car is almost undriveable. The car idles fine, but when you step on the gas, it gets real light and quickly wants to stall out. This requires feathering of the throttle to keep it from dying. The engine is a factory original 383 with cast iron intake and 4 bbl AVS carb. I checked my accelerator pump, and it's working OK. The car is a little low on vacuum, but doesn't appear to have a leak. I adjusted the timing both advanced and retarded, with no significant difference in the problem. It seems like either a weak spark or bad fuel/air mixture. Naturally the problem is the worst when the car is cold, then 'mostly' goes away once the car warms up. Thoughts?

Still sounds like the accelerator pump isn't squirting enough fuel.

Maybe too much of the idle transition slot is uncovered by too much idle speed screw adjustment? Or too lean of idle mixture?

Sounds like a typical Carter to me, try richening the idle mixture.

Sound like a typical intake vacuum leak to me. Especially if it gets worse when the engine is cold.

Just tightening the intake bolts won't fix it either.

Try pulling the vacuum advance hose, let the motor have more air, then put your finger over the tip of the hose to see if there's a change in idle at all. I'll bet it's the same since there's a vacuum leak elsewhere.

It could be the carb, maybe not, or a ruptured vacuum advance diaphram, only way to know is to start ruling some things out with some basic tests.

I've got a can of carb cleaner! I might have to start testing...

Does anyone know where to buy new vac advance and choke diaphragms?

grab a vacuum gauge while you are at it. If it was working fine and then acted up I'd say it's fuel blockage or leak.

OHHH and check the fule line from the sending unit to main line. If it has a smallllll crack that will happen, ask me how I know