[nkaminar]

There is a great site for Zenith carburetors at http://model-a.org/symptoms.html

Here is what they say about stalling at stops:

Engine dies when vehicle comes to a stop

Common Causes

• Float is set too high or a pin hole absorbs gasoline into float.
• Compensator Jet Orifice contains dirt or rust, or is too small.
• Idling Jet Orifice contains dirt or rust, or is too small.
• Idle Air Adjust Screw is mis-adjusted or too short, collapsing spring before it seats.
• Throttle Idle Adjustment Screw is mis-adjusted.
• Upper Casting Idle Jet Passage is restricted to Idle throat port.

There are other discussions about carburetor problems.