Need recommendation for a Carb for better MPG!

Unless if you are inferring to a "Smart Car", I think most cars are heavier today than the pass. My truck is 6,500 lbs and I believe the Challengers and Chargers are in the 4,500 range, thats about 1,000 lbs. more today for each.
Those are heavier for sure. There's a lot of thin gauge steel and plastic parts in the new cars. Even so, the heavy ones get decent mileage because of the efficiency and the transmissions. I could put a 8 speed auto in my Swinger and probably get mid to late 20's for mileage. Same with a 6 speed manual in my 66 Dart 273 car. A 833 o/d will get mid 20's. The new cars may weigh a bit more because of all the safety features. They are also well insulated for sound than the old cars were. My 66 weighs right around 3000# where my wife's Buick Envision weighs somewhere over 3500#. I haven
t compared size but both take up roughly the same space in the garage. Just a rough comparison, not like comparing a Suburban and a Honda Civic.