There are a bunch of threads on float level setting. 7/16 rod gap is the spec. While in there, verify no grit is inside the needle valve holding it open.
I’m not sure how this could be your issue though. If the slow running screw is not having an effect, it has to be because it’s getting so much mixture from somewhere else that the the amount the screw can add/subtract is negligible. That would have to be the valve. The only way to really verify valve seating is unfortunately with the carb off the car.