My Brum Scott did 70 mpg and it didn’t have an easy life. The 1932 Scott I ride now, with a blind does 50 per gallon at 50 to 55 mph. If I ride slowly it uses slightly more fuel being more efficient at higher speeds. Some years back a friend had a Scott that was heavy on fuel. He offered me a ride and straight away I could tell it wasn’t a happy engine, the mixture was too rich.