In a grain unloading system for a combine harvester a grain bin includes a frame, the frame has a floor with a trough. An unloading auger is disposed at least partially within the trough. An auger cover at least partially covers the auger. The auger cover has a hat for a top portion of the auger cover and a pair of gates movable between the hat and locations on the floor that are proximal to the trough. A gate adjustment structure is coupled to the pair of gates to move the pair of gates relative to the auger. A control system is coupled to the gate adjustment structure and configured to control the gate adjustment structure.
