The aircraft had been sitting outside in the weather since its last annual inspection on 12/1/84. After purchasing the aircraft, the pilot (who is an aircraft and powerplant maintenance technician) examined it and a ferry permit was issued by FAA for the proposed ferry flight to the pilot's home base. Unknown to the pilot, the main fuel line to the rear engine was partially blocked by a foreign material. This blockage allowed adequate fuel flow for a sustained static operation at 1000-1500 RPM and a brief burst of power at full throttle. However, it was inadequate for a sustained high power setting and as a result during the initial climb the rear engine power reduced to a level of 1200-1500 RPM. The pilot was unable to maintain flight and he headed for the nearest available landing site. He lost flying speed while pulling up to avoid trees at the edge of the site and the aircraft then mushed to a touchdown with a resultant hard landing.