I agree with Gus68, it's a choke issue. Most likely the carb was adjusted to operate with the damaged bimetallic strip. Now it is running Super Rich on start up, or going to full choke when it is not needed . ( If your in a heated garage or a warm area choke should set to partial, not slam to full choke ) Choke rod was also most likely mis-bent to compensate for the problem with the bimetallic strip. The low idle screws may also have been messed with for the same reason. A mis-tuned Rochester can drive you crazy. Just as a properly tuned one purrs like a kitten, in my opinion.