On March 17, 2006, approximately 0910 eastern standard time, a Loehle P5151, N151RG, piloted by a private pilot, was substantially damaged when it landed hard during a forced landing at South Lakeland Airport, Lakeland, Florida. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The pilot, the sole occupant aboard, received minor injuries. The local flight was originating at the time of the accident. The pilot stated the accident flight was the first flight of the day, and that he planned to fly locally before returning to the airport. Engine start, taxi, and pre-takeoff checks were uneventful. The airplane lifted off runway 32 at 65 mph and climbed at 80 mph. During the climb, approximately 120 feet above the ground and when the airplane was about three-quarters down the runway, the engine lost power. The pilot lowered the nose and observed trees straight head. He "banked slightly to the right and then started a smooth left bank towards runway." The pilot said he "waited about 1 second too long" before flaring. The airplane landed hard, collapsing the left main landing gear and shearing off the left wing. The fuselage broke in half behind the cockpit. On May 8, 2006, the Rotax 582 UL engine was disassembled and examined at Lockwood Aviation Supply, Sebring, Florida. In attendance were the National Transportation Safety Board and Rotax. Some of the discrepancies noted were: (1) the clutch system was aftermarket (non-Rotax) and the friction plates were worn and loose; (2) the exhaust system had been was modified contrary to installation requirements; (3) placement of the EGT probes were not of the required distance from the exhaust port (according to the installation manual); (4) fuel lines had been routed contrary to installation requirements; (5) required factory vent holes were not in the carburetor vent tubes, and the vent tubes were less than 50% of the effective area required to vent the float chambers; (6) carburetor retaining sockets were over-torqued, extruding the rubber gasket from under the clamping band; (7) the throttle cable return springs had been shortened, and the jet springs adjusted to the leanest fuel flow position. After installing a propeller and alternate gearbox, the engine was started but full power could not be achieved. After removing the fuel vent tubes from the carburetor float bowl, the engine was restarted and full power was achieved without difficulty. It was Rotax's opinion that the lack of correct venting of the carburetor float bowl caused the loss of engine power during takeoff.