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Yes, that's a PCV valve. That requires a 3/8" hose to a place that provides full time (manifold vacuum). You'll also need a "breather" on the other valve cover that goes to the air cleaner. Is your air cleaner stock?
Edit: is that a manual choke? Do you have it hooked up?
2nd edit: you may only have one 3/8" vacuum connection on that carburetor. It's probably being used by the brake booster. You also appear to be using ported vacuum for the distributor advance, which is probably not the best way to run vacuum advance, but it's probably not a huge problem.I don't think either thing is causing the issues you're seeing however.