On July 30, 2004, at 1800 central daylight time, a Piper PA-24, N5769P, collided with trees during a forced landing in Rockville, Indiana, following a loss of engine power. The private, instrument-rated pilot received minor injuries. The airplane was substantially damaged. The 14 CFR Part 91 personal flight was operating in instrument meteorological conditions. An instrument flight rules flight plan was filed, but it had not been activated at the time of the accident. The flight originated from Butler Field (IN46), a private airstrip in Rockville, Indiana, about 1700. The pilot stated he departed IN46 and attempted to contact Terre Haute International (HUF) Approach Control to activate his flight plan. He stated he was having problems with the radio. He was able to hear the controller, but the controller was unable to hear him. In a telephone interview the pilot reported he was in instrument meteorological conditions so he decided to return to IN46. The pilot stated he was in the traffic pattern to land on runway 09 when the engine lost power. He stated he thought he had picked up carburetor ice, so he applied carburetor heat, but was unable to regain any engine power. The airplane contacted trees and settled into a heavily wooded area near the airport. The pilot spent the night in the airplane and was able to find his way out of the woods the following morning. The weather reported at HUF, at 1753, was 1-1/4 mile visibility with light rain and mist, scattered clouds at 400 feet and a broken cloud ceiling at 700 feet. A post-accident inspection of the airplane was conducted by inspectors from the Federal Aviation Administration, Indianapolis, Indiana, Flight Standards District Office. This inspection revealed that the venturi on the air inlet side of the carburetor was blocked by a 5-1/2 inch long piece of heat shield material. This material covered about 70 percent of the inlet area. The source of this material could not be determined as it was not used anywhere on the airplane. The last annual inspection of the airframe and engine was performed on February 20, 2004, approximately 60 flight hours prior to the accident.