Leaky carb aside, did some more running/testing today. Moved the mixture screw out another half turn before I started. Engine ran quite a bit smoother today, actually.
But....
* It will NOT run smoothly (or at all) at a slow idle, but sounds pretty decent at a fast idle.
* It will ONLY run at partial choke, even when warmed up.
* If I even touch the throttle, it will die almost immediately.
Got myself a vacuum gauge today. Will get some readings tomorrow. But thought the detectives here might be able to offer a rough diagnosis with those symptoms.
My baseless theory is vacuum leak at the intake.