On August 2, 2012, about 1028 central daylight time, a Beech E-55, N3644A, sustained substantial damage when it struck a road embankment following an aborted takeoff after a loss of engine power on the left engine at the West Houston Airport, Houston, Texas. The pilot and his passenger were not injured. The airplane sustained substantial damage to the left wing. The aircraft was owned 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 operated on a flight plan. The local flight was originating at the time of the accident. The pilot reported that during the initial portion of the takeoff, the engines accelerated smoothly and the systems and gauges indicated normal operation. As the airplane accelerated the pilot noticed a roughness in performance and verified that the throttle, mixture, and propeller controls for both engines were forward. Due to the roughness and a perceived loss of engine power on one engine, the pilot aborted the takeoff. There was insufficient runway remaining to stop the airplane and it went off the end of the runway and struck an embankment that bordered the airport perimeter road. Postaccident examination of the airplanes left engine revealed damage to two of the six spark plug leads. The engine was mounted on a test stand and during a subsequent test run the engine exhibited rough operation. The damaged ignition harness was replaced with the harness from the right engine and the test run repeated. During the second test run the engine started immediately and ran through various power settings with no hesitations, stumbling or interruptions in power. The reason for the damage to the ignition harness could not be determined. The most recent annual inspection of the airplane was completed on July 16, 2012.