AFB Tuning

Bewy said
I am not sure if the 500 cfm model has velocity valves [ weights ] in the secondaries. That looks like a factory carb.

What model is it?
Four digit # should be stamped on one of the mounting feet.

Does the carb have a large brass screw in between the idle mixture screws?

I can see one problem: it looks like it has a single plane intake.

Is the engine stock?

Stock 273 Commando 4 speed Carter AFB. They have very light weighted velocity valves. All 273's use the same velocity valve with the large cut out on the counter weights. The larger valve is from a big block car or aftermarket AFB for comparison.