The pilot was taking off from the 020 degree grass strip but was using only the last 700 feet of the available 2200 feet. Partial engine failure occurred when the takeoff roll was well established. The engine surged. The pilot applied carburettor heat, full rich fuel mixture and full throttle without regaining full power. The pilot continued the takeoff and became airborne. He advised that he had to turn to avoid trees. The aircraft stalled from somewhere between 50 and 100 feet. The wings were damaged. The engine was pushed back into the firewall and the undercarriage collapsed. The owner subsequently advised that no fault has been found with the airframe, engine or fuel system. He believes that the likely cause of the loss of engine power was carburettor icing. Significant Factors The following factors were considered relevant to the development of the accident: 1. The engine suffered a partial engine failure probably because of carburettor icing. 2. The pilot did not reject the takeoff.