The intermittent loss of engine power due to a "stuck" stepper motor in the No. 2 engine's fuel control as a result of an inadequate overhaul. Contributing to the accident was the pilot's decision to continue flying the helicopter with a known defect, his decision to depart with the helicopter over its maximum gross weight, and his decision to fly the approach to the oil platform at a high gross weight in a direction that provided limited go-around potential.