During the 1st takeoff roll, there was a loss of engine power and the pilot aborted the takeoff. He taxied back and ran up the engines. The left engine was run up three times until the 'puffing (or popping) noises' were no longer heard, and the pilot commenced another takeoff. Witnesses reported hearing one or more engines sputter during the initial climb. The pilot reported that he lost left engine power within 300 ft AGL. He made a steep bank left turn back toward the airport, lost control, and collided with the ground. The left engine and carburetor assembly were successfully test run. Clear, blue colored fuel was found in the left engine's carburetor and gascolator, and in the right main fuel tank. Cloudy, green colored sediment laden fuel was found in the right engine's carburetor, and in the right engine driven and auxiliary fuel pumps. A foreign substance, which was laboratory identified as being polystyrene, was found adhered to the inside of the right engine's venturi.