carb prob

i got a sucking sound coming out of my carburetor, im guessing its a vacuum leak? its a 64 nova w/ rochester monojet. i pulled the hose off the round gold piece and put my thumb over it and i heard all the sucking stopped and my car died lol. its idling really low to begin with, and i got this big hissss sucking sound coming out the hole in the top of the carb.