I agree with Dave, it sounds like your idle to mid-range transition is lean. The first thing is to get your jets & metering rods right for your engine, and once it's jetted right you should be able to take any stumble out with accelerator pump adjustments. Edelbrock has some good Tech videos that they suggest you watch once you've selected your carb, to walk through the tuning process, link here - Edelbrock.com - Tech Center - Carburetor Installation and Tech Videos