At a height of about 350 feet after a normal takeoff, the engine commenced to run roughly. The pilot considered that the problem may have been caused by part of a propeller blade becoming detached. Power was reduced and the pilot commenced to turn back towards the aerodrome. A substantial amount of height was lost during this turn, and the aircraft was seen to make a number of lateral oscillations. It then struck the ground in a tail low, wings level attitude at relatively low forward speed. No pre-impact mechanical defect was found with the engine or propeller. However, initial examination of the wreckage revealed that the fuel selector valve was very close to the "Off" position. Tests conducted on a similar aircraft indicated that with the fuel selector positioned as found, sufficient fuel was available to allow engine operation at low to moderate power settings. It was considered likely that on this occasion the fuel flow required for take-off exceeded the amount available through the selector valve. This in turn led to an excessively lean mixture, and the engine lost power. The aircraft had stalled during the attempted turn back towards the aerodrome, and the pilot had insufficient height in which to effect a recovery.