The pilot reported that the day before the accident, the engine experienced a loss of power "from apparent fuel starvation." On the day of the accident, the pilot reported that before the flight he inspected and modified the fuel system. The pilot stated that he "installed fuel hose directly from tank to carb, bypassing gascolator and fuel flow sensor." The pilot then ran the engine at full power for five minutes before takeoff. The pilot successfully took off on runway 25 and at approximately 500 feet above ground level, the engine lost power. The pilot turned the aircraft back towards the departure runway. While turning to line up with the grass along side the runway, the aircraft "sank out of the turn, collapsed left gear leg and bent left wing - landing in soft grass." The airplane came to a stop in the grass with it's nose on the ground and tail in the air. The pilot exited the airplane and pulled the tail back down. The pilot reported that he believed the malfunction was a "fuel flow fault." Approximately 12 gallons of automotive fuel was on board at the time. Federal Aviation Administration airmen records indicated that the pilot does not hold airframe or powerplant mechanic certificates.