I believe that you are talking about the vacuum port for the vaccuum break diaphragm. Its part of the choke system that locks the choke linkage. It works in conjunction with the heated choke coil spring You probably do not have this anymore. Its a big diaphragm on the side of the carb.
If you have a manual choke, then cap this vaccuum port.
Cap all of the unused vaccuum ports.
AND don't forget the RAG trick.