THE AIRPLANE SUSTAINED A PARTIAL LOSS OF POWER (MECHANICAL MALFUNCTION) DURING THE INITIAL CLIMB OUT FROM THE AIRPORT AT NIGHT. WITNESSES REPORTED HEARING THE ENGINE SURGING AS IT PASSED OVER OR NEAR THEIR LOCATIONS. THE AIRPLANE WAS FLYING OVER UNSUITABLE TERRAIN TO THE SOUTH AND SOUTHEAST OF THE AIRPORT WHEN THE PILOT WAS FORCED TO LAND. IT COLLIDED WITH SEVERAL TREES AS IT DESCENDED THEN IMPACTED THE TERRAIN. EXAMINATION OF THE CARBURETOR REVEALED THAT ONE SIDE OF THE FLOATS WAS COLLASPED AND THE 'U' ARM WAS DISTORTED WHICH INTERMITTENTLY RESTRICTED THE MOVEMENT OF THE FUEL METERING NEEDLE. THE PILOT WHO RENTED THIS AIRPLANE JUST PRIOR TO THIS PILOT REPORTED A ROUGH RUNNING ENGINE ON TAKEOFF. THE OPERATOR WAS NOTIFIED. NO RECORD OF ANY CORRECTIVE MAINTENANCE ACTION COULD BE LOCATED WHERE THE AIRLANE WAS TAKEN OUT OF SERVICE.