On June 8, 2023, about 1219 mountain daylight time, a Piper PA-30, N7318Y, was substantially damaged when it was involved in an accident near Nephi, Utah. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed from Cedar City Regional Airport (CDC), Cedar City, Utah, to relocate the airplane to Skypark Airport (BTF), Bountiful, Utah, for an annual inspection. While in cruise flight, about 9,500 ft msl, the left engine rpm decreased from 2,400 rpm to 1,000 rpm briefly and increased back to 2,400 rpm. The pilot attempted to troubleshoot the left engine; however, it continued to cycle sporadically between 1,000 and 2,400 rpm. The pilot diverted to the Nephi Regional Airport (U14), Nephi, and initiated a straight-in approach to runway 17. During the landing flare, about 5 ft above the runway, the left engine lost all power. The pilot immediately applied right rudder to counteract the lowered left wing; however, the airplane touched down and exited the left side of the runway. The airplane subsequently impacted a dirt mound and came to a rest in an open field, resulting in substantial damage to the right wing. Postaccident examination of the airplane and both engines did not reveal any preimpact mechanical anomalies. The fuel system was traced from each wing tank to the carburetor at the engine through the fuel selector, which rotated normally and was unobstructed. The fuel lines that had not been damaged from impact or removed to transport the airplane were secure. Fuel sampled from the right strainer was tested with water-finding paste and revealed no water contamination. Removal of both the left and right fuel strainer bowls and filter discs revealed that the filter bowl and filter disc had contaminants consistent with rust/corrosion. The left and right fuel strainer knob assembly was removed, and corrosion was found in the cavity walls and cover plate. The left and right fuel selector valves were removed from the airframe and corrosion was found in the threads of the left and right fuel line auxiliary outlet unions. A follow-up examination of the fuel flow dividers and fuel servos did not reveal any mechanical anomalies or failures. The pilot stated about 7 months prior to the accident flight, the right engine fuel injectors were found obstructed during an inspection. Mechanical continuity was established throughout the rotating group, valvetrain, and accessory section as the crankshaft was manually rotated at the propeller by hand. Thumb compression was achieved at all four cylinders and the valves displayed normal lift when the crankshaft was rotated. Examination of the cylinders’ combustion chamber interior components using a lighted borescope revealed normal piston face and valve signatures, and no indications of catastrophic engine failure. According to the engine logbook entries from February 2, 2023, about four months before the accident flight, the right engine had a loss of power in flight. Troubleshooting found a restricted fuel screen and corrosion. The mechanic replaced both fuel screens and gaskets with new. He further replaced the right outboard auxiliary tank fuel line, flushed the fuel lines, and cleaned all fuel nozzles. The left engine’s fuel nozzles were cleaned and the fuel lines were flushed.