When I stop the car in traffic, it start stalling. This is prevented only when the carb line is disconnected. If the line to the car is connected and the line at the filter is disconnected, it would still begin to stall at the traffic light. This issue occurs if I drive normally to a stop or coast to it by braking. The distributor is replaced with a new one and carburetor has been rebuilt. What might be causing this stalling?
From the description it almost sounds like an air/fuel mixture issue. Possibly caused by unmetered air being sucked in at closed throttle. The vacuum system should be checked along with the intake manifold gasket. If no leaks are obvious, a smoke check of the induction system may need to be conducted. The evaporative emission valve should be checked as well as the evaporative emissions system. You may want to enlist the help of a mechanic, such as one from YourMechanic, who will be able to diagnose the stalling issue and have it corrected properly.