Classic/Antique Car Repair: 1951 Plymouth Cranbrook, 1951 plymouth cranbrook, vacuum advance

Question
QUESTION: Purrs like a kitten at idle, but can not hold a steady throttle. It is either Full out accelleration or idle.  Can't seem to keep an "in between" to keep the car running.  Any suggestions on what I can look for, clean, or do to help this problem?

ANSWER: Well lets see, if it will idle fine and accelerate that would appear to rule out the fuel pump and ignition coil. That leave the carburetor or a worn breaker plate in the distributor that is upsetting the ignition point setting when the vacuum advance kicks in. Just a question will it accelerate to full song when the gas pedal is kicked? Let me know.
Brad

---------- FOLLOW-UP ----------

QUESTION: Yes,slow acceleration or maintaining steady throttle is the problem.If you hold it one position it will backfire through exhaust sometmes.

Answer
It could be carburetion but sound more like a problem in the distributor when the engines vacuum increases at the vacuum advance and moves the breaker plate. It is possible that the pig tail wire from the points could be in a make and break condition acting up as the vacuum diaphragm moves the breaker plate.
Brad