On July 27, 2024, about 1331 eastern daylight time, a Piper J3C-65 airplane, N77522, was substantially damaged when it was involved in an accident near Groveland, Florida. The pilot and passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed in the airplane from Gore Airport (4FL9), Haines City, Florida with 17 gallons of fuel onboard, and flew about 1 1/2 hours before landing at Williston Municipal Airport (X60), Williston, Florida. During his attempt to refuel, he discovered that the fixed based operator (FBO) self-serve fuel pumps were out of order. The pilot calculated that the fuel remaining in the airplane was 11 gallons and departed on the return flight to 4FL9. After flying for about 1 hour, at an altitude of about 1,000 ft, the engine lost total power. The pilot attempted to troubleshoot but was unable to restore engine power as the airplane continued to descend, and the pilot performed a forced landing to wooded terrain. The airplane came to rest in a tree canopy about 31 miles from the destination airport. The pilot stated that he positioned the magneto switch and fuel selector to the Off positions before exiting the airplane. The airplane sustained substantial damage to its right wing and fuselage during the accident sequence. During recovery of the airplane, no fuel leaks were observed. About 28 ounces of fuel were recovered from the right wing and about 1/2 gallon was recovered from the left. Postaccident examination of the engine revealed impact damage to the engine and engine mount. Crankshaft and valvetrain continuity were established during manual rotation of the propeller. Both left and right magnetos produced spark during rotation of their drive gears. The oil sump contained about 3 quarts of oil and the filter screen was clear of debris. No anomalies were noted to the exhaust system. The throttle cable remained attached to the carburetor and continuity was established to the throttle lever. The carburetor was absent of fuel, and its fuel inlet screen was clear of debris. The propeller remained attached to the engine with no leading-edge damage or chord-wise abrasions noted to either blade. The airplane’s fuel system comprised two 8-gallon wing fuel tanks, a four-position fuel selector valve, and a Piper PA-18 header tank mounted below the instrument panel. The recovered fuel was clear of debris and absent of water. There was no fuel present in the gascolator bowl, and its screen was clear of debris. The fuel tanks were intact with no leaks or contamination found. The fuel caps’ vent tubes were clear of obstructions and were in the forward position. The fuel selector valve was in the Off position. Fuel line continuity checks revealed that when the fuel selector was positioned to the Rightwing fuel tank, continuity was established from the gascolator to the left tank, and when positioned to the Left tank, continuity was established to the right. There were no anomalies noted to the Both or Off positions. The header tank was intact and absent of fuel. The header tank’s lower port contained a T-fitting with lines that connected to the gascolator and fuel selector valve. The upper port contained an On/Off valve, noted in the On position, and the supply line to the primer. There were no other lines attached to the header tank. A review of the airplane’s maintenance logbooks showed that on February 01, 2021, the original fuel tank was removed and replaced by two wing fuel tanks in accordance with a Supplemental Type Certificate. The installation drawings were not made available during the course of the investigation. The mechanic who performed the installation reported that the fuel system was installed in accordance with a Piper PA-18 fuel system. Review of the PA-18 fuel system revealed that the primer supply line connected to the gascolator and the header tank’s upper port vented to the left fuel tank. Fuel records from X60 showed that the accident pilot made two transactions with no fuel dispensed. The airport manager reported that a placard on the self-serve fuel pump instructed users to contact the FBO if any fueling issues were encountered, at which time a fuel truck would be made available. There was no record of the pilot contacting the FBO for fuel. A postaccident search did not reveal any ADS-B or radar data for the accident flight. According to Continental Engine’s specification chart for the A65, at cruise power settings, the engine’s fuel consumption would be 4.4 gallons per hour. At this rate, the two flights would have consumed about 13.2 gallons, leaving about 3.8 gallons of fuel remaining. These calculations do not include fuel used during start, taxi, run-up, or takeoff and climb. Due to the airplane fuel system’s lack of documentation, the amount of unusable fuel was unknown.