i have a supermileage carburetor book in which a coupa designs are vacuum type carburetors. incredible mileage is possible if all gasoline is vaporized, but exposing gas under a vacuum or preheating it can be dangerous.
smokey yunick took an 80's chevy to a hundred MPG by preheating fuel.
think this is the link:
http://www.rexresearch.com/yunick/yunick.htm
personally i felt carburetors were never fully explored.
i once heard of a 70MPG carb having been left on a 70's dodge pickup and accidentally slipping off the assembly line...
chryser got wise to its mistake and offered a brand new top of line truck in exchange for carb alone - to no avail!