The 781-hour private pilot, was performing a maintenance test flight following the installation of four overhauled engine cylinders in his tail wheel-equipped homebuilt airplane. Following the break-in runs for the new cylinders, the pilot elected to depart the uncontrolled private airstrip. During the climb out, while climbing through approximately 2,000 feet mean sea level (MSL), the engine stopped producing power. After an unsuccessful restart, the pilot made a 180 degree turn in an attempt to return to the airport. When he was unable to reach the airport, the pilot elected to land in a pasture. While attempting to make the pasture, the airplane impacted a three foot levee at the edge of a rice field before coming to rest in an upright position. Inspection of the airplane at the accident site by a Federal Aviation Administration (FAA) inspector, revealed that the right fuel tank contained approximately 12 gallons of fuel, while the left tank was breached and appeared to be empty. The quantity of oil in the engine was found to be at "normal" levels. The reason for the reported loss of engine power could not be determined.