1973 Plymouth Scamp accelerating/braking issues, please help

Have you done anything else to the car? Any car history? What is the state of tune plugs/wires/fuel filter. Does it blow black when you are accelerating? I would start at the carb. I have seen needle valves stick after the car has sat awhile and the fuel evaporated cause similar behavior. Also is the choke staying open? I have had them slap shut going down the road and that is no fun. Most (95%) part store rebuilt carbs have issues of one kind or another.