To check if it is a vent issue try to connect both vents with a piece of tubing. If this stops the stalling then try a longer vent whistle. If it does not then your throttle plates are closing off completely. causing a very lean condition. Holley has a dashpot that keeps the throttle plates from closing down quickly.
http://www.holley.com/HiOctn/ProdLin...MSCA/11-4.html
Or try setting your idle speed a little higher.
Mike