On May 29, 2020, about 1130 central daylight time, a Piper PA-24-180, N6989P, was substantially damaged when it was involved in an accident near Humboldt, Tennessee. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, the airplane had been at Humboldt Municipal Airport (M53) Humboldt, Tennessee, for about 5 weeks to have new avionics installed in the airplane. The installation was completed on the day prior to the accident flight. The mechanic had also fueled the airplane to a total of 60 gallons that day. The purpose of the accident flight was to test and evaluate the new avionics. After the pilot performed a preflight inspection of the airplane with no anomalies found, he and the mechanic boarded the airplane for the flight. During the taxi and engine run-up, the pilot noted that “all engine parameters were indicating normal.” The pilot taxied to runway 22 and briefed the mechanic of his intentions to remain in the traffic pattern. After applying full engine power, he again noted that the engine instruments indicated “normal.” Shortly after lift-off the engine “shuttered and had a sudden reduction in RPM.” With the landing gear still down, he pitched the airplane forward, and the engine regained RPM, which brought the nose back up. After clearing over powerlines off the departure end of the runway, the engine backfired, shuttered and experienced a total loss of power. He then set up for a forced landing on a golf course. After touching down, he “applied maximum braking” before the airplane struck a wooden fence, and then a brick pillar and metal pool fence, which resulted in damage to the fuselage and both wings. Both the pilot and passenger egressed the airplane without injury. The airplane was recovered to a salvage facility and an engine examination was conducted by an airframe and powerplant (A&P) mechanic, with oversight by a Federal Aviation Administration inspector. The engine did not show evidence of impact damage and all components were present. No evidence of any preimpact mechanical malfunctions or failures of the engine were observed during the examination. A fuel sample was obtained from the carburetor bowl that appeared cloudy with a greenish-yellow tint. A second fuel sample obtained from the fuel supply hose was clear with a blue tint. A third sample obtained from the main gascolator sump was clear with blue tint. The electric fuel boost pump was powered on and functioned normally. The internal filter screen in the electric pump was clean with no debris. The mechanical fuel pump produced suction on the inlet side when the crankshaft was rotated manually via the propeller. The source of the fuel contamination was not determined.