THE PILOT, WHO DID NOT PERFORM WEIGHT AND BALANCE CALCULATIONS PRIOR TO TAKEOFF, ATTEMPTED A TAKEOFF IN AN AIRCRAFT THAT WAS OVER THE ALLOWABLE MAXIMUM GROSS WEIGHT. THE AIRCRAFT LIFTED OFF TWICE, BUT WOULD NOT CLIMB, AND THE PILOT ELECTED TO ABORT. HIS STOPPING DISTANCE WAS EXTENDED BECAUSE HE HAD TROUBLE BRINGING THE VERNIER TYPE THROTTLE TO THE IDLE POSITION. WHEN THE AIRCRAFT RAN OFF THE END OF THE RUNWAY, THE PILOT STEERED IT ONTO A NEARBY ROAD, BUT HE IMPACTED A TREE WHILE AVOIDING AN ONCOMING AUTO.