Engine issue - vacuum related?

[eighteenninetytwo]

Blazer (350 sbc) starts fine, but stalls as soon as I take foot off the gas irrespective of choke position - it will keep running if i rev it but I don't want to do that. Could be vacuum related? I have (what I think is ) an old vacuum canister with two ports, it has one line from the front left side of the Edelbrock carb but the other port on it isn't connected? Should that be connected to something and a tube came off maybe?

I'm pretty new at the engine stuff, just getting into it bit by bit so please excuse me if this is a retarded question. Google tells me this is supposed to hold a vacuum for brakes etc but wondering how it does that with an open port - hence my question.