64 Dart with 273 4-speed Carb

why no vacuum advance? Id check the mechanical advance plate for snappy action. When its idling crappy. stop motor and check fuel level in carb. must take the top off but its only 8 screws and a few clips. If its low then its a fuel delivery issue but usually a plugged filter or bad pump will cause trouble after a few minutes of idling or into a drive. It could even be flooding. See if the boosters are dripping fuel. thats a needle/seat issue or a electric pump with no regulator (blue or black holley)