idle issues

Good job on carburetor rebuild, your work was not wasted.

I still think you have a fuel delivery problem, check float level, fuel pump for output and pressure, and blow out fuel line. Stumbling, and backfiring up through carburetor is sign of lean condition, and sometimes incorrect timing. Often when a car sits un used for a while fuel lines can become gunked up with rust & varnish, perhaps pin holes which will inhibit pumps ability to deliver fuel, and pump diaphragms dry out or dry rot.