The above photo of my Sport Jet with the stacked center tanks, the upper tank has now been removed for the same reason, this engine simply doesnt need that much fuel. After approx 7 mins flying I return with 40% fuel remaining.
If you are using Jeti, Futaba or Multiplex with telemetry get hold of the Xicoy Engine telemetry module, it will give you perfect fuel remaining during your flight. I do not have a timer on any of my jets any longer, I fly to the amount of fuel I have. Very cool.