New to me 73 duster 340

Start with the basics, check the plugs to make sure they are the correct heart range, as mentioned set the initial timing 16-17* and around 37* total at about 2000 rpm. Get a vacuum gauge and hook it to the "manifold" vacuum port on the carburetor and tune the mixture screws for maximum vacuum reading. Take it out and drive it to see if those changes make any difference before tearing into the engine. Someone may have detuned it, "just because".