On June 16, 1993, at approximately 1113 central daylight time a Cessna 150L, N11069, sustained substantial damage when it impacted a fence and fence post during a forced landing following a loss of partial engine power. The solo student pilot sustained minor injuries. Visual meteorological conditions prevailed throughout the area for the solo cross country instructional flight. During interviews conducted by the Federal Aviation Administration inspectors with the operator, owner, pilot, and flight instructor, the following information was revealed. This flight was the first solo cross country flight for the student. The preflight preparation was completed by the student and the flight departed the Spring, Texas, airport at approximately 1050. During cruise flight, at 2,000 feet MSL, approximately 30 miles northwest of Spring, Texas, the pilot smelled fuel. A check of the flight surroundings and the cockpit area for smoke did not reveal a source. The student pilot stated that within a few seconds the right fuel gauge went to zero and the engine started running rough. Altitude could not be maintained and the pilot selected a field for an emergency landing. The flaps were extended ten degrees and the carburetor heat was pulled to the on position as the power was reduced to idle. During the landing roll the airplane hit the barbed wire and fence post, then cartwheeled along the ground, and came to rest with the nose down. An examination of the site by the Federal Aviation Administration inspectors did not reveal any evidence of fire. Flight control continuity was established and fuel was found in both fuel tanks. An examination of the engine and accessories by the inspectors and the engine representative (report enclosed) revealed the following information. The left magneto was not firing continuously and was firing in a random sequence. An internal examination of the magneto revealed a loose coil. Maintenance records reviewed by the investigator in charge indicated that on May 26, 1992, the new left magneto had been installed. The airplane was released to the owner following the investigation.