On July 31, 1998, about 1900 eastern daylight time, a Grumman American AA-1A, N9415L, was substantially damaged during a forced landing after it experienced an in-flight fire and loss of engine power near Point of Woods, Fire Island, New York. The certificated airline transport pilot and a passenger sustained minor injures. Visual meteorological conditions prevailed and no flight plan had been filed for the flight that departed Long Island Mac Arthur Airport, Islip, New York, destined for Republic Airport, Farmingdale, New York. The personal flight was conducted under 14 CFR Part 91. According to the pilot, he was flying parallel to the beach at 1,300 feet when he decided to demonstrate an engine failure and forced landing approach for the passenger. The pilot further stated: "...Upon termination of the demonstration [at 800 feet], I applied power to recover and the engine responded by running extremely rough with popping and coughing noises accompanied by an extreme vibration. I reduced power, checked the security of the primer system, the mixture rich, [I applied] carburetor heat on with adverse results. At this time smoke started entering the cabin, so I opened the canopy. I turned the fuel boost pump on and smoke intensity increased 10 fold. I secured the fuel boost pump and closed both cabin vents. However, smoke continued to fill the cabin...." The pilot performed a forced landing to the beach and during the touchdown, the airplane nosed over. Examination of the wreckage by a Federal Aviation Administration (FAA) Inspector 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 were observed. The carburetor was removed from the airplane and forwarded to its manufacturer, where it was disassembled and examined under the supervision of an FAA Inspector. The examination revealed an incorrect venturi, part number 46-F12, was installed in the accident carburetor. According to the carburetor manufacturer, the correct venturi part number was 46-F11. Review of the airplane's maintenance records revealed a two piece venturi was removed from the carburetor and a one piece venturi was installed about 50 hours prior to the accident.