On February 7, 2001, approximately 1500 central standard time, a Cessna 172S single-engine airplane, N980SP, registered to and operated by Louisiana Technical University, Ruston, Louisiana, sustained minor damage during a forced landing following a loss of engine power while maneuvering near Ruston, Louisiana. The certified flight instructor (CFI) and the student pilot were not injured. Visual meteorological conditions prevailed and a company visual flight rules (VFR) flight plan was filed for the 14 Code of Federal Regulations Part 91 instructional flight. The flight originated from the Ruston Regional Airport, Ruston, Louisiana. According to the CFI's statement, he and the student pilot were practicing power-off stalls in the local practice area. At 2,200 feet msl, the student pilot performed a "flow checklist (fuel valve on both, mixture rich), and had reduced power in order to slow [the] speed," to set up the airplane for a power-off stall maneuver. Shortly after these procedures were completed, the CFI noticed that the propeller was "slowing to a stop." Subsequently, the engine lost power, and the CFI performed engine restart procedures in accordance with the Cessna Aircraft Pilot Operating Handbook (POH). The engine failed to restart, and the CFI executed a forced landing to a field. During the landing roll, the airplane impacted a fence and came to rest upright near a tree line. On February 8, 2001, representatives from the FAA, Textron Lycoming, Cessna Aircraft Company, and the operator examined the airframe and the Lycoming IO-360-L2A engine (serial number L-28217-51A). Fuel samples were taken from the aircraft, and no evidence of contamination was found. The fuel injector inlet screen was clean, and there were no visible fuel stains around the injector, nozzles, lines, or fittings. The 4 lower spark plugs were removed, they had a black coloration, and according to the engine manufacturer representative, "the electrodes indicated a long service life." Under the supervision of the FAA inspectors, an engine test run was performed. The engine ran for approximately 8 minutes at 1,500 RPM, then, after reducing the throttle to the hard stop idle position, the engine experienced a total loss of engine power. As the engine lost power, black smoke exited the exhaust pipe. The engine was restarted, and black smoke exited the exhaust pipe. The engine speed was again increased to 1,500 RPM, the throttle was reduced to hard stop idle position, and the engine again lost power. The engine manufacturer representative adjusted the mixture control wheel, located on the fuel injector unit, "eight turns toward the lean setting." The engine was restarted, and when the throttle was reduced to hard stop idle position, the engine continued to operate. As a result of this incident, the flight school checked their C-172 fleet and found several aircraft idle mixture controls out of adjustment. The required mixture adjustments, in accordance with the applicable Lycoming Service Instruction, were completed, and the aircraft were returned to service. Additionally, the flight school began requiring each pilot-in-command to perform pre-takeoff and post flight idle mixture leaning checks and record the RPM indications on every flight. During the pre-takeoff check, if the RPM fluctuation is out of the prescribed limit, the flight is to be rejected. Also, the flight school modified the emergency engine restart procedures based on time and altitude permitting.