On April 11, 2005, at 1345 Pacific daylight time, an experimental single-seat Clark Aerosport Scamp (ARSPRT SCMP WT 16-3), N234HC, made an off-airport forced landing after a loss of engine power during the initial climb from Chino Airport, Chino, California. The commercial pilot sustained minor injuries. The airplane sustained substantial damage. The pilot, also the registered owner and builder of the airplane, was operating it under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight was originating from Chino at the time of the accident for the local area test flight. According to airport operations personnel, the pilot had just departed runway 26L. During the initial climb, he reported a partial loss of engine power. The pilot maneuvered the airplane to land on runway 3, but landed just east of the runway in a field. During the landing roll, the airplane nosed over inverted. The Federal Aviation Administration accident coordinator responded to the accident site. The airplane was a bi-wing airplane equipped with a Volkswagen engine. The engine was crushed aft toward the cockpit and the wings had collapsed on one another. The empennage section was crushed. Emergency response personnel plugged the fuel tank in order to prevent fuel from draining onto the ground. The airplane and engine had accumulated approximately 6 hours total time and were going through their Phase I flight testing. The pilot reported that just prior to the accident flight, he adjusted the mixture setting on the carburetor. Previous flight tests indicated that the mixture was running too rich. He contacted the carburetor manufacturer and was advised to adjust the control no greater than one full turn. The pilot adjusted the setting one complete turn. Prior to takeoff, he performed a test run at 2,700 rpm with no anomalies noted. Normal operation is at 3,600 rpm. When the airplane reached 300 feet above ground level (agl), the pilot realized that the engine was not developing full power, and he leaned the mixture attempting to correct the problem. The condition worsened and he continued, approximately 200 feet above ground level. The airspeed began to decay so he elected to land the airplane in a field. The pilot did not report any mechanical failures.