On August 21, 1993, about 0825 central daylight time, a Taylorcraft BC12-D airplane, N5486M, experienced loss of engine power during climb from takeoff and descended to ground collision near Custer Park, Illinois. The flight instructor and student aboard incurred serious injury. The airplane was substantially damaged. Visual meteorological conditions existed in the vicinity. The instructional flight originated without a flight plan and operated under 14 CFR 91. The flight commenced from the private sod strip where the airplane was stored outside. There was no commercial fuel source on the airstrip. The airplane contained a mixture of automobile gasoline and aviation fuel. The owner transported automobile gasoline to the airstrip and, on each second or third flight, purchased aviation fuel at an away location. The left wing and fuselage header tank had been topped with automobile gas before takeoff. The instructor and student recounted sampling fuel at the drain points and the gascolator before flight. The student started, taxied and took off to the east. About 150 feet above ground, and before the end of the runway, the engine quit abruptly. The instructor took the controls, felt buffet and lowered the nose. He stated he considered obstructions on runway heading (power lines and a bridge) and trees on the right with tops above him. He stated he decided to spin the airplane to the corn field beneath them rather than collide with the obstacles. The airplane turned a half revolution to impact. Examination of the airplane revealed a pink foreign material in the fuselage fuel tank, fuel shutoff valve and gascolator. The wings fuel tanks contained none. The material in the fuselage tank and valve appeared as a plastic solid. Material sealed within the gascolator flowed slowly and hardened to a solid after several days' removal from fuel. Laboratory analysis identified the material as polystyrene. The tank in which the owner carried fuel to the airplane showed none of the pink material. An origin of the foreign material was not found.