fish carb stories have been around for a while. but there has never been any good scientific test to support that they actually work.

as devils advocate, an engine requires X amount of fuel to put out Y amount of power. granted it can be leaned out for better economy so long as there is complete combustion. however (lots of them with fuel mileage huh?) there is hardly ever a "complete" burn which is where hydrocarbon emissions come from, the most complete burn comes from a gaseous fuel, rather than a liquid fuel which is what the fish carb is supposed to do- extremely atomize the fuel to make it closer to a "gas"

there is propane, but just like alcohol, it has very different qualities, such as BTU/pound and octane rating. our engines that are intended for gasoline are not optimized for these other fuels, which is what causes alot of disappointments with lower fuel economy.

fuel injection can meter the correct amount of fuel to maintain a given air/fuel ratio, but like alot of automotive systems, it is more optimized for emissions than it is for fuel economy. in a nut shell: best emissions happens at 14.7 stoichiometric, but fuel economy is better around 16.5. the problem? the higher combustion temeratures (that also like to eat up engine internals) produce too many NOx, or nitrogen oxides (which help create acid rain)

aftermarket computers can be tuned for fuel economy, while still being able to have the proper enrichment for acceleration. but your not gonna find that tune on a factory computer. and while a carb would have a low initial cost, the time and additional equipment to tune it to safe levels for those air/fuel mixtures would not make it very feasible for the average consumer. and it is still nothing more than an organized leak...

the closest that i have seen to an atomizer from a trusted source was smoky yunicks fiero that used a low speed turbo. which is an interesting read that I hope to test on someday.

I probably went off topic a bit, and I apologize. I am kinda biased towards fuel injection...