['68OrangeSunshine]

You need to clean your carb, then adjust it. Edelbrock kit 1477 covers the AFB type.
Ask Edelbrock for a Performer Carb Owner's Manual. They're free.
The smudge at the back of the carb suggests a manifold leak -- which would manifest as your stall symptoms. Once rebuilt, with a fresh gasket, you should get a good seal.

I have a Edelbrock 1404 [500 CFM] on my 292 L6 in the '68 C/10, and a Carter AFB 9635S [600 CFM] on the 350 in my '71 GMC Jimmy.
[When Federal Mogul stopped selling Carter carburetors ~2000, Edelbrock still made them as ''Performers''. Same carb, built in the same Weber plant, just different marketing.] The AFB 9635 approximately equals an EDL-1405.