Flight Details
The aircraft was in level flight and cruise configuration when the pilot reported that the engine suddenly began to run rough. The pilot noted that when power was partially reduced, the roughness terminated. When the mixture was leaned, the engine died momentarily.
Engine Roughness
During the event, the pilot reported that engine RPM was maintained at approximately 2450 RPM, but only 15 to 18 inches of manifold pressure could be obtained. The roughness persisted intermittently during the flight.
Landing and Damage
On short final approach to a selected field, the pilot remembered to switch the position of the fuel selector. Following this action, power returned to a normal level and the roughness disappeared. The pilot then elected to proceed to another, more suitable landing site. During landing at this second site, the aircraft was substantially damaged.
Post-Accident Examination
Subsequent examination of the aircraft and engine revealed no mechanical malfunction of any engine or aircraft component that could have caused the transient engine roughness the pilot repeatedly experienced.