I should add that my Galaxie has a 390ci V8 with an electronic distributor, a 750 double pumper carb with vacuum secondaries, a Blaster coil, an open element air filer, copper wires, SplitFire plugs, electric water and fuel pumps, and it gets 31mpg on the freeway at around 70mph.
My ‘clean’ Volvo gets 26mpg going downhill with a tailwind at 55mph.
“a 750 double pumper carb with vacuum secondaries”
What brand of carburetor would that be?
Double pumper carburetors do not need vacuum secondaries.