Welcome Aboard !

On ALL vehicles with carburetors, especially older ones....
• The quality of the air filter is THE number 1 key to good fuel economy when your engine has carbs. Carburetors work by an extremely delicate balance of air flow and vacuum. A shoddy replacement filter, or an old or clogged filter easily upset this balance. Original equipment was Purolator or Mann.
• Older Airheads with the open air scoop atop the starter cover are famous for having mice nests inside the starter cover and/or air filter cover, which has the same effect as issue #1. Evict the mice !!
• Unless you know for a fact this has been done, then I highly recommend that you replace the needles and needle jets inside the carbs. The needle meters the fuel in the mid-range, but is also exposed to the pulsing air within the venturi. After 40 years of air pulse induced hammering the needle gets smaller and the needle jet gets larger... thus metering out more fuel than is needed. (You will also want the latest model ethanol-proof float needles and floats installed at the same time.)

Other Airhead tuning tips....
• Run the highest octane fuel you can find. And it needs to be fresh. You need to read about and study Top Tier Fuels. https://www.toptiergas.com/licensed-brands/
• Old ignition parts is a perennial issue. Replace the plug wires with METAL core wires, replace the spark plug caps with NGK 5K Ohm caps, and get some new NGK BP7ES plugs.
• Double check your mechanic and strobe time the engine at 5000 RPM. At high RPM the "F" timing mark should be dead center of the timing window.
• If you drive around below ~3000 RPM, then STOP. Use the gearbox and get the revs up. The Airhead engine FEELS like a "chugger", but it's not.
• While inside the carbs, use a caliper to insure that both needles are protruding the same amount from the carb's slide. Bing uses a crazy "blind" design that does not allow you to directly check the needle position. Thus is it common (without measuring) to have needles in different notch positions and not know it.
• Fill the tires up! Sounds silly, but newer tire technology requires 10-15% more air pressure in the tires than what the owners manual recommended back in 1975. Try 35F and 33R.

These are all common, spare time, owner-maintenance tasks you should be able to do over the course of the next several months.

Hope this helps. 🙂