Gas Mileage Issues

Reading between the lines, I would say you need a major tune-up, and do it by the book. The points opening and closing is just not good enough. They need to be set. Look for vacuum leaks like bad hoses and such. Advance hose needs to be on proper port. Cap and rotor need to be in good condition and not cross firing. Plugs need to be gapped, and wires need to be in good condition and in the proper order. Clean air cleaner. Maybe run some cleaner thru the tank or re-build carb if it won't respond to tuning. Synthetic oil can help, but you won't get your money back on just mileage. There is more, but on top of all I wrote, you need to figure out if the trans is slipping, or possibly the clutch. Mileage will suffer a lot in these cases, and you won't go much farther.