Okeh, so the underhood configuration is non-stock. That valve, called the EGR (exhaust gas recirculation) valve, did not appear until 1973. There was no provision to mount it on 1972 intake manifolds.
The presence of the air pump says your car was built for sale in California; non-CA '72s did not have the air pump. They
did have a seriously awful full-time exhaust gas recirculation system with no valve, described
here. Those cars were not happy runners, particularly not at their high-and-rough idle.
But your intake obviously has provisions for an EGR valve, which has clearly been removed and a blockoff plate installed. With a new gasket, it's to hope. Very fine. What (specific) carburetor do you have? Not just "Holley" or "Holley 1920", but which
exact one? The number is stamped on the carb body above the float bowl, which is the rectangular part at the front.
The rhythmic (rather than randomly lumpy) roughness in the vid suggests a couple of possibilities. Top of the list: at least one of your valves could be set a bit too tight. Follow the
valve adjustment procedure. Next on the list: one or more single-cylinder vacuum leaks; this usually means a faulty seal at the manifold-to-head gasket junction. It is very much worth your while to get the
good gaskets for the manifolds-to-head and intake-to-exhaust junctions. Take a careful look at your spark plugs when you pull them (and take/post a clear, sharp, close pic of all six of them lined up in 1-2-3-4-5-6 order); if there's a vacuum leak in a cylinder or two, it'll show up on the business ends of the plugs.
Another possibility is an incorrectly-chosen or stuck-open PCV valve. Many differently-calibrated ones look and fit alike; an incorrect, faulty, or poor-quality one can cause shaky idling.
Your idle speed sounds like it's set too high, perhaps to the high speed specced for California '72s to prevent them stalling with that no-valve EGR setup. Go set your idle speed and mixture and your basic ignition timing as described
here in this post and see if that also helps smooth things out.
Beyond that, Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted
here for free download, and you'll want to look at the tune-up parts and technique suggestions in
this post.
I'd recommend deleting (removing) the air pump and its associated plumbing and brackets. You'll need to plug the holes at the rear of the cylinder head. This will greatly reduce underhood temperatures, which will help numerous aspects of driveability. Consider doing the
fuel line mod and the
HEI upgrade to further improve how the car runs.
No. You should not smell exhaust inside the car, full stop. If you do, that is dangerous. Find and fix the exhaust leaks and the body leaks. Make this your top priority so you get to stay alive. The first link earlier in this comment describes some common leak points, including one specific to '70-'72 exhaust manifolds (which your car might still have despite the '73-up intake).
