On August 22, 1995, at 1513 hours Pacific daylight time, a Navion A, N8513H, crashed in an open area while executing an emergency landing about 1/2 mile west of Pine Mountain Lake Airport, Groveland, California. The emergency landing was required due to a total loss of power. The pilot was beginning a local visual flight rules maintenance test flight. The airplane, registered to and operated by a private individual, sustained substantial damage. The certificated commercial pilot and his passenger, a certificated private pilot, received serious injuries. Visual meteorological conditions prevailed. The pilot, also a certificated airframe/powerplant mechanic, reported in the aircraft accident report that he had been working on the airplane hydraulic system; the left main landing gear would not retract. The pilot said that the passenger, a certificated private pilot and airframe/powerplant mechanic, was performing mechanics duties only. The pilot said that shortly after flying over the end of the runway (the left main landing gear retracted normally), the engine began to misfire. He said he glanced at the fuel selector valve and saw that it was in the normal position and he cycled the electric fuel boost pump, but without success. He said that the engine sounded as if the cylinders were firing at the wrong time. The pilot elected to execute a 180-degree turn to return to the airport. He said that his last action in controlling the airplane was to bank it to the right to avoid hitting an oak tree. The owner's father said that he observed the accident. He said that as the airplane flew over the end of the runway, between 150 and 200 feet above the ground, the engine ". . . seemed to fade out and the airplane lost altitude. . . ." The airplane then entered into a steep right turn and stall. It crashed in a field about 1/2 mile north of the runway end and came to rest facing 090 degrees. The on-scene investigation was conducted by the Federal Aviation Administration (FAA), Fresno [California] Flight Standards District Office. The investigating inspector reported that he did not note any defect with the engine, or any engine components. The inspector said he found the fuel selector valve placed between the main and auxiliary fuel tank position. On October 10, 1995, the carburetor was flow-checked and disassembled, and the fuel selector valve was examined at Carburetor Airmotive, Burbank, California. The carburetor external examination disclosed that the inlet attach fitting and the mixture lever were broken. The fuel discharge nozzle was bent. The technician was unable to connect the inlet line to the discharge nozzle, and he replaced the mixture assembly before conducting the test. The fuel selector valve was found seized near the closed position. The flow testing showed the carburetor operating in a lean mixture setting. Test point No. 2 could not be taken due to extensive damage to the fuel discharge nozzle (see Carburetor Fuel Flow Data herein this report for a detailed listing of the test flow data). The disassembly examination disclosed that the mixture control was bent and seized near the idle cut-off position. The poppet valve stem contained some rust. The inlet fuel screen was free of contaminates and the venturi body was normal. The base of the carburetor displayed impact damage and was bent.