On November 15, 2021, about 1012 eastern standard time, a Mooney M20M, N21890, was substantially damaged when it was involved in an accident near Tampa, Florida. The private pilot and one passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that he flew the airplane earlier that day on an uneventful 15-minute flight from Peter O Knight Airport (TPF), Tampa, Florida, to Lakeland Linder International Airport, Lakeland, Florida. After landing he picked up his passenger and departed for Gainesville Regional Airport, Gainesville, Florida. At 3,000 ft mean sea level (msl) with the mixture control full rich and the engine operating at 32 inHg and 2,400 rpm., he noted the turbine inlet temperature (TIT) was in the red range. At the same time of the high TIT reading, he noticed liquid on the bottom portion of the windshield. He confirmed that the mixture control was full rich and reduced engine power, which decreased the TIT reading, but there was still liquid on the windshield. While at 4,000 ft msl, he advised air traffic control of the higher temperature and diverted to TPF, maintaining 4,000 ft msl until on the downwind leg of the airport traffic pattern where he reduced power, extended the landing gear and lowered the 1st notch of flaps. He turned onto the base leg, and at 1,200 ft above ground level before turning onto final, he added throttle, but the engine did not respond. He pushed the mixture, propeller, and throttle controls full forward, which at full throttle automatically turned on the auxiliary fuel pump, but noted the propeller was windmilling. At 800 ft msl, he realized he would be unable to make the runway and told his passenger about the impending ditching. He retracted the landing gear and maintained a nose-up wings level attitude ditching the airplane. Both occupants exited the airplane and were transported to land. The underside of the fuselage was substantially damaged during the ditching. Following recovery of the airplane, examination of the fuel lines in the engine compartment revealed the inlet fuel line at the manifold valve was 7.5 flats of the b-nut from being hand tight against the inlet fitting. There was no provision for safety wiring the b-nut and there was no torque stripe on the b-nut or inlet fitting. Pressure testing of the fuel supply system was performed with the b-nut in the as-found position revealed fuel leaked at the b-nut. After the b-nut was tightened, no leakage was noted at the b-nut. Inspection of the threads of the fitting and of the flexible fuel hose revealed no discrepancies. Torque stripes were noted on the fuel injector nuts at the manifold valve. Review of the maintenance records revealed that nearly 2 months before the accident, fuel system components consisting of the engine-driven fuel pump, servo fuel injector, manifold valve, and fuel injectors were removed for testing and overhaul. The components were installed and according to the pilot, the airplane had been operated about 12 hours over 3 or 4 flights since installation. There was no record of any subsequent engine work after the overhauled components were installed. The mechanic who installed the components after testing and/or overhaul reported that the airplane owner helped with the installation. The mechanic also indicated that he normally would have applied a torque stripe to the inlet hose at the manifold valve.