Factory Fuel Gauge-Go buy a piece of dowel,then empty the tank,,with tank on bike. Add one liter of fuel ,put dowel in lowest part of the tank every time and mark on the dowel.Repeat until tank is full. At track add fuel,, measure on your dowel ,,do laps record the number of laps and measure fuel used. This way you never drain the tank trackside.
But remember a race with no body to ride with will use less fuel then if you are dicing with someone.Also if you lap time changes so does fuel consumption.