You can do a crude test of the mechanical advance in the distributor by removing the cap and grasp the rotor and turn it by hand. You should feel the counter weight spring tension as you turn the rotor, and it should snap all of the way back when you release it.
Generally, that should be done before one digs into a carburetor. No matter in your case, since you discovered an issue with your carburetor. I still recommend checking everything related to spark timing, before doing any more carburetor work.
Carl
