On Saturday, July 2, 1994, at 1400 eastern daylight time, a Cessna 172N, N734TU, piloted by Thomas Oliver and operated by Emerson Aviation, Inc., sustained substantial damage during a forced landing near Bristol, New Hampshire. The pilot received minor injuries, and the two passengers were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was operated under 14 CFR Part 91. The sightseeing flight was maneuvering at 2500 feet, when the pilot reported a loss of engine power. There was insufficient engine power to sustain flight; therefore, the pilot established a forced landing to the nearest field. During the landing roll, the nose gear collapsed and the firewall was damaged. Mr. Sylvester Dye, a Federal Aviation Administration Airworthiness Inspector, examined the airplane. He found a rag in the carburetor heat duct. The airplane had flown three flights since the completion of an annual inspection.