If it is loading up in the midrange, you need to screw the brass regulator screw in to lean the midrange. Get it running about 3-4K, and listen. If it slows and loads up, the regulator is too rich. If it speeds up it is too lean and the regulator needs to be screwed out.

The "stock" position is the head of the brass regulator screw just flush with the aluminum case.

Remember, the brass screw isn't a pump, it's just a pressure regulator.