Lynn,
750 double pumpers are race carbs. They have rich main jets, about 5 steps higher than regular street carbs. The problem is that if you dejet it 5 steps the engine will run lean at low manifold vacuum because the Pvcr ports in the power valve circuit are undersized. What you need to do is either get a new carb or reduce the size of the main jets and drill the pvcr ports in the metering block.
Go to this website, it will guide you a bit. I also suggest getting a book on Holley carbs.
http://www.bob2000.com/carb.htm
Matt