An employee was replacing a starter generator bracket on a gas-powered golf cart. This required removal of the starter. He removed the seat to gain access to engine compartment and knelt on the floorboard of the car to get into position to perform the task. He loosened the starter generator adjustment bolt so that the starter generator belt could be removed. After loosening the adjustment bolt, he began to pull the belt off the front pully on the starter generator. At the same time, his knee pressed the accelerator pedal on the car. This caused the starter generator to be energized and it began to turn catching his left middle finger between the pully and the belt resulting in a partial amputation.