If you're not getting black smoke out the exhaust after it warms up and the plugs aren't fouling AND you don't smell fuel on the dipstick and the oil level isn't gradually rising I'd leave it alone. Be aware though that if mechanical fuel pumps
rubber
parts start to fail it can put fuel in the crankcase, affect mileage and wash down engine cylinders (not good) - so that is what those last two checks determine. If you really want to delve into that issue here is a video that's enlightening, you can skip to about 6:30 minutes into the video to see how oil dilution can occur:
Also if somebody modified the rear grea ratio, mileage will be affected; simple to check and there are several Youtube videos that show how to determine that ratio by turning a rear wheel and counting driveshart revolutions. And yes, "Hot Rod Harry" types would increase
carb jet sizes and play other games to try to get a performance boost at the expense of mileage when gas was eighteen cents a gallon; I see it a LOT on vintage Corvette carbs.