Sequence of Events
A pilot reported that the engine had been 'running rough' since a 100-hour inspection. The engine had accumulated 130 hours total time. During the run-up, the engine was misfiring until the pilot leaned the mixture and allowed it to fully warm up. After this, the engine performed normally.
Takeoff and climb to cruise were uneventful. Approximately 45 minutes into the flight, the engine RPM dropped. The pilot initiated corrective procedures, including switching fuel tanks, which restored power momentarily. The engine then began misfiring and backfiring. The pilot attempted further corrective procedures, but the engine lost total power. The pilot executed a forced landing in a football field.
Post-Mishap Inspection
During a post-mishap engine run-up, the engine performed normally.