Event
During a demonstration of an engine failure and forced landing to a passenger, the pilot applied power at 800 feet above ground level to recover. The engine responded with extreme roughness, including popping and coughing noises accompanied by vibration. Application of carburetor heat and use of the fuel boost pump aggravated the situation. With smoke entering the cabin, the pilot executed a forced landing on a beach. During the touchdown, the airplane nosed over.
Investigation
Examination of the wreckage revealed fire damage in the area of the carburetor air intake box. The airplane's fuel lines were intact, and no evidence of fuel leaks was observed. Disassembly of the carburetor disclosed that an incorrect venturi, part number 46-F12, was installed. The correct venturi part number for the carburetor was 46-F11.
Maintenance Records
Review of the airplane's maintenance records indicated that a two-piece venturi had been removed from the carburetor and a one-piece venturi had been installed approximately 50 flight hours prior to the accident.