Jeff,

The large brass screw adjusts the regulator diaphragm. It's supposed to be adjusted so that the engine is running at peak RPM with the high-speed needle at one turn out.

The return line will open only when the engine's running at low throttle and the pump is moving fuel. A spring on a check valve keeps it closed otherwise.

Usually, fuel will move through the pump only when it's turning. You can't really blow through it and expect any results.