On October 16, 2005, approximately 1615 central daylight time, a single-engine Cessna 140 tail wheel-equipped airplane, N72901, was substantially damaged during a forced landing following a loss of engine power while maneuvering near Big Flat, Arkansas. The private pilot and passenger were seriously injured. 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 and a flight plan was not filed for the local flight. The airplane departed the Gastons Airport (3M0) near Lakeview, Arkansas, at approximately 1600 en route to the Dennis F Cantrell Field Airport (CWS) near Conway, Arkansas. The 345-hour private pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that he completed his preflight inspection and determined that he 26 gallons of fuel on-board for the flight. He then departed for CWS, approximately 17 nautical miles away, to pick up a passenger. The pilot then departed CWS for 3M0, about 76 nautical miles away; no problems were experienced during these flights. However, ten minutes after departing 3M0, the pilot reported having "engine trouble and a loss of RPM". The pilot reported that "he ran the emergency checklist and searched for a place to land," but was unable to maintain altitude. A Federal Aviation Administration (FAA) inspector examined the airplane at the accident site, and noted that the airplane impacted the ground on its right side after coming through trees in a heavily wooded area. In a telephone conversation with the NTSB Investigator-in-charge, the owner stated that he owned the airplane for approximately two years. Additionally, he stated they only ran aviation fuel in the airplane (the airplane had decals near the fuel caps, allowing the use of automotive fuel). The owner added, that the airplane had experienced several loss-of-engine power events before, but each time the pilot was able to make a safe landing. The first time was shortly after buying the airplane; an inspection of the airplane's fuel tanks, revealed contamination in the form of "beads" in the tank. Shortly after having the tanks flushed, the second loss-of-power event happen (after each event, and after the airplane had landed the engine would produce power again). The carburetor "was looked at," and the airplane returned to service. Approximately 15-30 hours later, another loss-of-power event happened. This time the carburetor was sent-out for overhaul. The repair facility rebuilt the carburetor and told the owner that the "wrong jet" had been installed in the carburetor. The owner stated that since the rebuilt carburetor had been installed, the airplane had flown about 50-60 hours without any problem, and figured the problem had been finally resolved. This Cessna 140 has two fuel tanks (one in each wing). The wing fuel tanks are vented by "vent holes" in the fuel caps. The accident airplane's original fuel caps were replaced sometime prior to the accident. The fuel caps installed on the airplane were an aftermarket design, with the label "2646V" inked on the top of the caps. The vent holes on these caps, were found to be less than half the size of the original fuel caps vent holes. Additionally, it was possible for the gasket (in the fuel cap) to cover one or both of the vent holes. The owner stated that he had not replaced the fuel caps, and they were on the airplane when he bought the aircraft. A review of the airplane's records failed to reveal when the original fuel caps were replaced. The reason for the power loss could not be determined. At 1555, the automated weather observing system at Marion County Regional Airport (FLP), approximately 15 miles southwest of the accident site, reported calm wind, 10 statute miles visibility, a clear sky, temperature 77 Fahrenheit, dew point 48 degrees Fahrenheit, and an altimeter setting of 30.10 inches of Mercury.