Circumstances:
With the wind from the right rear quarter at seven knots and 15 degrees of flap selected the pilot attempted a downhill take-off from a one-way 390 metre grass strip. The aircraft was about 100kg below maximum all up weight with the right fuel tank full and the left tank half full. The pilot reported that he flew the aircraft clear of the ground at an indicated airspeed of 50 knots after approximately two thirds of the strip length. Shortly after becoming airborne the stall warning sounded, and the aircraft yawed violently left. The aircraft collided with a fence before coming to a rest about 200 metres from the departure end of the strip. The pilot indicated that the aircraft became airborne at too low an airspeed and that this coupled with the fuel imbalance and the tail wind resulted in a loss of control.