When Model As were being produced, only “straight run” gasoline was available with an octane rating of 60-70. Today’s gasolines / fuels will do just fine and well tuned engine should deliver fuel economies of around 20 + miles per gallon. The Model A Ford boasts one of the most straight forward and dependable fuel systems ever designed. A casual examination of the illustration will serve to emphasis the gravity feed concept. The fuel flows downhill from the tank to the carburettor. To ensure that we do get a good supply of fuel to the engine there are several areas that we should not overlook.
Click on the link to read the complete article 
Fuel supply newsletter 2010