What about "blowing the carbon out" on the freeway b4 getting a car smogged? (861/2 Nissan carb) not injected. Does it really do any good for a short drive city car? What about putting in hi test fuel for the test?

It's called an "Italian tune up", and yes, it can work. Also put in high test fuel and one can of gumout one and done cleaner in the tank