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If pumping the gas pedal keeps the car running, the likely cause of the problem is dirt or sediment in the carburetor bowl. If enough sediment accumulates, it can block the jets that fuel flows through out of the bottom of the bowl. Pumping the gas pedal lightly causes fuel from the accelerator pump to enter the engine, making up for the loss of fuel from the jets.
A carburetor rebuild will correct the problem you are having.