On September 3, 1995, at 1853 eastern daylight time (edt), a Patin Challenger II, N4281P, piloted by a private pilot, was substantially damaged when it collided with an electrical power line and the ground during a forced landing. The pilot reported a partial loss of power shortly after takeoff. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 flight was not operating on a flight plan. The pilot reported serious injuries. The flight departed Cedar Springs, michigan, at 1850 edt. Witnesses stated that N4281D's engine began sputtering shortly after takeoff. They said the airplane began circling back to the restricted landing area for what they thought was a landing. The witnesses said as the airplane approached the landing area its tail wheel engaged an electric power line. They said the airplane pitched down and collided with the ground shortly after the wire contact. The on-scene examination was conducted by a Federal Aviation Administration Principal Maintenance Inspector (PMI). The PMI said observed flight control system continuity on N4281D. He said an examination of the engine revealed four fouled spark plugs. Two of the spark plugs were fouled to the point that there was no visible gap. A representative of the engine manufacturer stated the required spark plugs for N4281D's engine were the NGK B8ES type. He said the plugs should be discarded after 25 hours engine operating time. The pilot/owner said his spark plugs didn't have to be changed until they had operated for 50 hours. The PMI asked the owner how many hours he had on the spark plugs. The owner said the plugs had close to 50 hours on them. N4281D's engine had the NGK B8ES plugs installed in it at the time of the accident. The manufacturing representative said the engine must be decarbonized after every 50 hours of operation. According to the representative, the engine's cylinder heads, cylinders and pistons must be removed for examination and cleaning. The pilot/owner told the PMI that he checks for carbonization by viewing the piston through the exhaust port. The manufacturer's representative said this method is not reliable and should not be used. Excerpts from the manufacturer's operator's manual for N4281D's engine are appended to this report.