Need recommendation for a Carb for better MPG!

Then that right there is the telling point of your experience. None. The 318 has always been a good mileage motor. The small bore lends itself well in that arena. I can tell first hand you don't know what's goin on here.
Show proof of good gas mileage for the 318's. I never said that they didn't or couldn't get mileage I was simply talking about my own personal experience.