On June 13, 2011 about 0900 central daylight time, a Vans RV-6A, kit-built airplane, N80WW conducted a forced landing, after experienced a loss of engine power while in cruise flight near Colgate, Oklahoma. The private pilot, sole occupant, received only minor injuries. The airplane was substantially damaged during the accident. The airplane was registered to and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan. The flight originated about 0800, from the Mount Pleasant Regional Airport (OSA), Mount Pleasant, Texas, en route to Harper, Kansas. The pilot reported he departed on the cross-country flight with the airplane’s fuel tanks full; the initial departure and first part of the cruise flight was uneventful. About 40 minutes into the flight, he noticed that the engine’s exhaust gas temperature (EGT) climbed from 1380 F to 1400 F. The pilot subsequently enriched the mixture slightly and the temperature dropped back to 1380 F. The pilot then stated that everything appeared fine; however, approximately 2 minutes later, the higher EGT indication reappeared. The pilot then again enriched the mixture slightly and the EGT reading dropped back to normal. The pilot added that the same circumstances repeated itself a couple more times. Finally, after enriching the mixture all he could, the pilot stated “the engine quit as though someone closed the mixture in a routine shutdown, without any sputtering or coughing”. Unable to restart the engine, he selected a field to conduct a force landing in. During the forced landing, the airplane’s landing gear collapsed and the airplane came to rest in an upright position. The airplane was recovered to the owner’s hangar for examination. On July 28, 2011 an investigator from the NTSB and the airplane’s owner examined the airplane. The airplane’s wings and fuselage had sustained heavy damage during the forced landing; the nose landing gear had folded back into the firewall and cabin area. The engine’s carburetor located at the bottom of the engine had sustained impact damage and was broken from away from engine’s sump/intake. Additionally, the carburetor itself was broken by the impact and remained attached to the airplane by the alternate air cable. Both mixture and throttle control attachments were pulled from the carburetor. The carburetor finger and airplane’s fuel line gascolator screens were absent any contaminates or debris. Both fuel tanks were breeched during the accident; air was blown into the fuel line and through the fuel selector towards the fuel tanks. The fuel lines and fuel tank pickup points appeared clear without abnormalities. The engine driven fuel pump was partially disassembled and no abnormalities noted. A reason for the loss of power was not found.