[Gaz64]

Looking at your carbs, I'd put money on it the bowls have the late model umbrella inlet valve, it took over the early design because it would be way cheaper to mass produce.

The early bowls had a hanging ball inlet valve that would shut when the pump operated. The inlet valve was open at rest, so the pump circuit could not develop pressure.

The umbrella inlet bowl "may" have a .013 hole in parallel with the inlet valve. It's purpose is as above, allows percolation bubbles to vent to the bowl and not pressurise the accelerator pump circuit.

If it doesn't have the hole, I would add it, it makes the accelerator pump a little less sensitive to gentle opening rates, so the car may use less fuel, and not load the plugs up as much from light throttle driving.