On April 28, 2004, at 1800 central daylight time, a Cessna 150G, single-engine airplane, N493RA, registered to and operated by a private individual, sustained substantial damage during a forced landing following a loss of engine power while maneuvering in the vicinity of Livingston, Texas. The private pilot and one passenger were not injured. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The local flight originated from the Livingston Municipal Airport (00R), Livingston, Texas, at 1705. According to the 175-hour pilot, after take off he climbed to approximately 1,000 feet above ground level (agl), and flew in the local area about 50 minutes. After making several circles around the airport, the engine started to run "rough." The pilot applied carburetor heat and maneuvered the airplane to set up for a forced landing into a field. He reported that the engine "appeared" to be starved from gas, and as he cycled the throttle, the engine would "restart." After several attempts to maintain engine RPM, the engine "quit." Subsequently, the pilot landed the airplane in a grassy field located across from the airport. During the roll-out, the front tire struck a small ditch, nosed-over, and came to rest inverted. An examination of the wreckage by a Federal Aviation Administration (FAA) inspector, who responded to the accident site, revealed that the firewall was buckled. Both wing fuel caps appeared to have their respective vents "painted over," and when low pressure air was introduced to the left wing fuel vent, the vent appeared to be blocked. Higher pressure air was applied to the vent, and a "pop" was heard, as if the vent had "cleared" debris when the air was applied. According to entries in the airplane's maintenance logbooks, the last annual inspection was completed on March 15, 2003. Additional entries showed that the airplane had flown a total of approximately 1.4 hours (including the 50 minutes of the accident flight) since the annual inspection.