On November 9, 1999, about 1000, eastern standard time, a Cessna 150, N8323G, was substantially damage during a forced landing in New Hope, Pennsylvania. The pilot, who was not injured, held a private pilot certificate with a glider rating, and was working on a single engine airplane rating. Visual meteorological conditions prevailed for the solo flight that originated from the Twin Pine Airport, Pennington, New Jersey. No flight plan was filed, and the flight was conducted under 14 CFR Part 91. According to the pilot he arrived at the airport about 0845, the day of the accident, and began to preflight the airplane. During the preflight he noticed no anomalies. He remembered both fuel tanks were half full, and that they corresponded to the fuel quantity gauges inside the cockpit. The pilot then boarded the airplane, and started the engine on the first attempt. He let the engine warm-up before taxiing short of runway 30 to complete the engine run-up checks. The run-up checks were normal, and the pilot taxied the airplane onto the runway. He then completed three touch-and-goes before departing the traffic pattern. Because of a local agreement with air traffic control the pilot climbed to 500 feet msl, then to 800 feet msl, before starting a climb to 1,500 feet msl. While climbing through 900 feet msl, the engine started running rough. The pilot applied carburetor heat but the problem persisted. Unable to maintain altitude the pilot identified a field which appeared to be flat. He maneuvered the airplane to the field, and then experienced a total loss of power. The airplane touched down smoothly, but then encountered rising terrain. The nose gear collapsed, and the airplane came to a stop. According to a Federal Aviation Administration Inspector, the engine primer was found in the unlocked position, and the fuel tank vents were blocked by mud deposited from insects. In addition, the carburetor bowl was empty. After the Inspector removed the filler caps from both fuel tanks the carburetor bowl filled with fuel. With the engine still attached to the airframe, the Inspector performed an engine run. The engine started , and operated "normally." The owner's manual states that during a preflight to check both fuel tank vents for blockage.