During cruise the engine experienced a momentary surge with rough running and a decrease in engine speed to 1200 RPM. The pilot stated that he carried out all emergency procedures but the engine failed to respond and regain power. A forced landing was carried out onto a beach, but during the landing roll the nose wheel entered soft sand and broke off at the fork. One propeller blade and the nose cowls also suffered damaged. The fuel system was checked and found to be free of contamination, the fuel was of the correct grade with sufficient on board for the flight. The engine was inspected, and then test run successfully with no apparent faults found which may have caused the engine to lose power, although a later inspection found some contamination in the fuel injector distributer valve. The reason for the engine to lose power could not be positively determined.