The non-certificated pilot reported flying the unregistered amateur built Quad City Challenger I at 1,300 feet msl, when the engine "stopped cold." During the forced landing, the airplane struck a power line, and sustained substantial damage to the left wing and fuselage. The pilot inspected the contents of the fuel tank, and found no contamination. He removed the fuel bowls from the engine's dual carburetors and found them to be full of fuel. He was able to rotate the engine by hand and believed the engine stoppage was caused by an ignition failure. The Challenger I was an ultralight-type aircraft equipped with a Rotax 503 engine. The Rotax 503 Operators Manual stated, "This engine, by its design, is subject to sudden stoppage. Engine stoppage can result in crash landings, forced landings or no power landings. . . . This is not a certified engine. It has not received any safety or durability testing, and conforms to no aircraft standards."