On April 12, 2014, at 1100 central daylight time, N2788H, an Ercoupe 415-C, sustained substantial damage when it made a forced landing after a partial loss of engine power shortly after takeoff from Tenkiller Airport (44M), Cookson, Oklahoma. The pilot and the pilot rated passenger were both seriously injured. The airplane was registered to and operated by the pilot. No flight plan was filed for the flight that was destined for a private airstrip in Etna, Arkansas. Visual meteorological conditions prevailed for the personal flight conducted under the provisions of 14 Code of Federal Regulations Part 91. The pilot rated passenger stated the first takeoff attempt had to be aborted due to a loss of engine power. He and the pilot taxied the airplane back to the departure end of the runway and cleared the engine by applying full and partial power several times. The pilot rated passenger said the engine seemed to be performing well and departed. Shortly after becoming airborne, the engine began to lose power and the pilot made a left turn back toward the runway. The pilot was unable to maintain altitude and landed in wooded terrain. There was no post-impact fire. A witness, who was a friend of the pilot, provided a statement similar to that of the pilot rated passenger. He also said the pilot had a rough running engine on takeoff the day before the accident and quickly landed. The pilot was unable to duplicate the problem on the ground but noted that the header tank had overflowed. The witness and the pilot then opened the cowling and saw that a large amount of fuel had evaporated and residual fuel stains were observed around the carburetor. The witness then got in the airplane, started the engine and did several high speed taxi-runs with no engine problems. He elected to takeoff and made two full-stop landings. On the second landing, the witness said the header tank began to overflow. The pilot consulted the airplane's manual, and read that a loose gasket in the gas cap might be the cause of the fuel overflowing and tightened the gasket. The next day, the witness asked the pilot if tightening the gasket had resolved the problem and he said it did. A postaccident examination of the airplane wreckage revealed that all of the fuel tanks were breached and a small amount of fuel was found in the header tank and gascolator. The carburetor inlet fitting was broken from impact and there was no fuel found in the carburetor bowl. The mixture control was disconnected from the carburetor and was not safety-wired in the full-rich position. The top spark plugs were removed and the No.1 and No.3 plugs were black. The engine was manually rotated via the propeller and valve train continuity was established on each cylinder. Inside the cockpit, the primer was found unlocked and partially pulled out. Fuel was also found in the primer line to the carburetor. The airplane's last annual inspection was completed on February 1, 2014, at an airframe total time of 2,235. The airplane had accrued 15 hours since this inspection. The private pilot certificate for airplane single-engine land. His last FAA third class medical certificate was issued in November 2008 and his last biennial flight review was conducted in November 2009. The pilot reported a total of 850 flight hours, of which, 300 hours were in the same make/model as the accident airplane. The pilot rated passenger held a private pilot certificate for airplane single-engine land. His last FAA third class medical was issued in May 1979. He reported a total of 500 flight hours, of which, 30 hours were in the same make/model as the accident airplane.