holly carb question

Sounds like it needs to rebuilt again. It's likely the accelerator pump isn't working right on your hesitation problem. That's easy enough to check with the carb still on the car. With the engine off, pull the air cleaner off and look down the throat of the carb and work the throttle linkage. There should be a squirt of fuel each time you open the throttle. Other trouble areas on that 1920 carb are the metering block, float, leaks, and adjustments. If you're only getting 10MPG, it's either running real rich or you have some tune up problems such as retarded timing, missing, or bad compression in one or more cylinders.