The pilot said that the flight departed runway 30 and at about 900 feet during the initial climb the engine power level smoothly reduced to about 2,000 RPM. The pilot noted that there was no roughness associated with the power loss. The pilot said she was concerned about the nature of the terrain ahead and elected to perform a 180 degree turn and land down wind on runway 12. The aircraft touched down about two thirds of the way down the runway and the pilot thought the aircraft could not be stopped prior to colliding with a fence at the runway end. She said she added all available power and the aircraft lifted off and over the fence. The aircraft then settled back to the ground and collided with two coral fences about one quarter of a mile beyond the end of the runway. The pilot said the winds at the time were from about 310 degrees at about 10 knots. The engine and airframe were examined by FAA airworthiness inspectors who did not find evidence to explain the reported loss of power.