Fuel

That may not be enough. There is usually a small pot in the middle of the tank that the pump sits in. That is to prevent the fuel from running away from the pick-up screen when the level is low and you go around a corner. When the engine is running, that pump is kept full of fuel. When you run out, you need to put enough in that fuel is high enough to run over into that pot to fill it. In some cases that can be almost 1/3 of a tank.