Often, more fuel economy may be gained AWAY from the engine:

http://www.thecarburetorshop.com/Troubleshooting.htm#Fueleconomy

The two largest fuel mileage increases I acquired on my current shop truck were: (1) replace the dogmatic transmission with manual - 26 %, and (2) remove the bug screen - 21 %.

Changing from a Holley 2-barrel to a Carter 4-barrel picked up about 15 percent, and replacing the Carter 4-barrel with TWO Carter 4-barrels another 6 percent. (No, it isn't a stovebolt 6).

Jon

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop