On August 4, 2016, about 2030 eastern daylight time, an amateur-built PA14EXP airplane, N18PG, sustained substantial damage when it struck a fence and nosed over during a forced landing following a loss of engine power during initial climb after takeoff. The pilot and passenger received minor injuries. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which was not on a flight plan. The local flight was originating the Paul C Miller-Sparta Airport, near Sparta, Michigan, at the time of the accident. The pilot reported that he performed a pre-flight inspection of the airplane and a run-up prior to takeoff. All checks were normal. He stated that the takeoff was normal until reaching about 300 feet above ground level when the engine lost all power. He stated that the engine was still rotating. He checked the fuel selector, which was on "both", and attempted to pump the throttle which had no effect. He then executed a forced landing to an adjacent field, but stuck a fence with the landing gear. The airplane came to a rest on the ground past the fence. The airplane was an amateur-built version of a Piper PA-14 airplane. It was powered by a reciprocating carburetor equipped Aerosport O-375 engine bearing serial number 1547-SPE. The engine was rated to produce 205 horsepower. According to the pilot report the engine had accumulated 45.5 hours total time in service at the time of the accident. The engine was examined by Federal Aviation Administration inspectors while still mounted in the airframe. All engine controls were still attached and functioning normally. The carburetor was broken at the flange mount. All fuel hoses were intact and unrestricted. The fuel strainers and screens were clean. The engine was rotated and compression was noted on all cylinders. Six quarts of oil was present in the engine. The battery was connected and ignition spark was checked. Spark was observed, but the inspector noted that the spark "seemed weak". No anomalies were noted. Subsequently, the airplane owner had the engine removed and sent to an engine rebuilder where it was placed in an engine test cell and was run for about 5-6 hours. During the testing the engine was run with the electronic magnetos that were installed at the time of the accident, but a surrogate carburetor was used since the one that was installed at the time of the accident had broken during the accident sequence. No anomalies were noted during the engine test run. At 2053. the weather conditions reported at the Grand Rapids International Airport included a temperature of 28 degrees Celsius and a dew point of 18 degrees Celsius. According to a carburetor icing probability chart, the reported temperature and dew point were in a range for moderate carburetor icing at cruise power settings and serious carburetor icing at descent power settings.