Incident Overview
A pilot reported that during preflight inspection, he checked the full fuel tanks for water at all three access points and found none. The engine ran smoothly during taxi, run up, and takeoff, but stumbled upon level off. The pilot switched fuel tanks and checked the carburetor heat, noting that the engine only smoothed out with full power. He decided to return to the airport. On the base leg, the engine lost all power, resulting in a forced landing in a cornfield.
Postflight Examination
A Federal Aviation Administration inspector examined the airplane and found no obvious mechanical anomalies with the engine's physical components. However, inspection of the carburetor fuel inlet filter revealed it was approximately 75 percent blocked with particulate matter, including large quantities of rust, insect remains, and sand. The report noted that a restriction of this amount would significantly affect the engine's ability to operate at lower power settings and could result in a total loss of engine power.