What happened
Approximately seven minutes after reaching cruise altitude, the pilot transitioned from the right fuel tank to the left fuel tank. The engine continued to operate for roughly seven more minutes before stopping. Upon switching back to the original fuel tank, the pilot observed the engine power surge before it stopped again. An attempt to restart the engine was unsuccessful.
The pilot performed a landing in a muddy field on the aircraft's main landing gear. Shortly after touchdown, the airplane nosed over. During the landing, the main landing gear tires became caked with mud, though no mud was present on the tailwheel.
The investigation
An on-scene investigation confirmed engine control continuity and determined that the ignition system met all manufacturer operating specifications. Regarding fuel levels, approximately 7 gallons of fuel remained in the left tank, while only about 1 quart was found in the right tank. The gaskets on the fuel tank caps showed no signs of damage. However, investigators discovered traces of dirty water within both the carburetor float bowl and the fuel strainer.
Findings
According to the FAA's Flight Training Handbook, a soft field landing in a tailwheel airplane should be executed such that the tailwheel touches down at the same time as, or slightly before, the main landing gear tires.