I'm averaging somewhere over 20, probably 24 or so (I don't keep track of it right now). I'm not using much gas.
I used to get 24-27 m.p.g. when I kept track of my mileage.
Just stay away from the bad gas. I put some gas with 10 per cent ethanol in my car last week, and my car started misfiring, and the mileage tanked. As soon as I put Chevron super unleaded (with a bottle of STP) in the car, she started running like a real car again.
re: carbs: the mechanic replaced mine the second year I had it. It was getting to where he really couldn't tune the car right (neither could I). A new carb will make a difference, but I'd get new plugs, cables, rotor, cap, etc. first. Good spark plugs help. I've heard mechanics say that bad quality spark plugs will affect the performance of the car. I've used Bosch and NGK in mine.