[rotorwrench]

The GAV is the trim adjustment control for the high speed jet circuit in the carburetor. Adjust during cruise for best overall running down the road. The only other adjustments to it would be for higher or lower altitudes or temperatures. The idle circuit takes care of idling and it should be adjusted for best running at idle or best manifold vacuum if you have a MAP gauge.

Timing is very important. You want the spark to be able to reach the full measure of advancement as recommended by Ford Motor Co's publications but an operator of one of these cars has to know when to retard the spark not only for starting but also for pulling a load up a hill. Nothing is automatic on these old cars so it all has to be done by the operator to get best mileage.

The type of terrain can also make a difference. A car will get the best mileage in relatively flat land situations and at relatively slow speeds compared to modern highway speeds. How the milage is measured can also have an effect. The old speedometers need to be accurate or a GPS should be used unless it is a closed course of know distance values.