AFTER DRAINING THE MAIN WING FUEL TANKS FROM AN AIRPLANE THAT HAD BEEN PARKED FOR SEVERAL MONTHS, THE NON-CERTIFICATED PILOT DEPARTED FROM AN AIRSTRIP ON A LOCAL AREA FLIGHT. DURING THE TAKEOFF CLIMB, THE ENGINE POWER REDUCED TO IDLE AND THE PILOT PERFORMED A FORCED LANDING. THE AIRPLANE COLLIDED WITH TREES, SHEARING OFF THE WINGS. A POST-ACCIDENT INSPECTION OF THE AIRPLANE REVEALED THAT THE GASCOLATOR WAS FROZEN. THE PILOT LAST OBTAINED A STUDENT PILOT/MEDICAL CERTIFICATE IN 1981; HOWEVER, HE REPORTED HAVING ACCRUED 1,860 FLIGHT HOURS.