Make sure the timing is set correctly…The Motorcraft / Autolite 2V carb has a “power valve” which has a vacuum operated rubber diaphragm. If the rubber diaphragm fails, the valve opens to the “power” (rich) position at all times, destroying gas mileage. But 12 or 13 is all you will ever get but that’s a LOT better than 8…
Your question to your mechanic: Do you know how to rebuild a Motorcraft 2-barrel carb??
38,000 miles…That’s 300 miles a year average…HHHHhhhMMMmmmmmm