This urban myth has been going around for decades, as has been stated above. The Fish carburator from the 1940s was another one. During WWII there was gasoline rationing so naturally a myth like this would surface. People not educated in chemistry, physics or engineering tend to fall for the conspiracy theories.

The most efficient gasoline engines ever produced were the big (3350ci) 18 cylinder radials used in the DC-7 airliner. They used 145 octane leaded gas and "Power Recovery Turbines" that took waste exhaust heat and converted it to mechanical energy geared back into the crankshaft. The Bendix injection carburator was similar to the optional, and troublesome, mechanical fuel injection setup on 1957 Corvettes. That car certainly did not get 200mpg.

Jim