OK i'm late to the game here, sorry if this is stale, redundant, annoying, etc....
i can verify that your seat-of-the-pants instinct is correct -- evaporating fuel in the carb/intake is isothermic, eg. takes a lot of heat to evaporate the gasoline. i actually *measured* it --
http://worldpowersystems.com/AMC/195.6OHV/Intake/
scroll down to "fuel charge temperature".
the catch is -- the fue::air mixture doesn't hang around very long at all in the intake system between carb and intake valve, and i am personally not convinced that any system will add heat to the mixture, assuming that your goal is to reduce droplet size on it's way to combustion.
Smokey Yunick was concerned with this, in his later adiabatic engine experiments. but the motor industry has gone another way from that, and achieved great results. which doesn't necesarily mean Smoley was wrong; "industry" cares most about cheap and repeatable.
i think overall it's *velocity* that does the most good; the carb (or FI/EFI) system makes smallish droplets, the intake delivers them to the cylinder, they swirl and burn. the tiny burning planets of fuel, if given enough time (THAT'S THE BIGGEST CATCH!) release all their energy.
the fact of "open throttle == cool fuel" to me tells the whole story. the velocity (feet/second) would be easy to calculate, and that time, in milliseconds, is how long you have to impart heat energy to the gasoline droplets.
