On October 17, 1999, about 1830 eastern daylight time, a Cessna A185E, N85PR, registered to Outback Seaplanes, Inc., experienced a loss of engine power and in-flight collision with a tree while descending for a forced landing near Lake Wales, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 personal flight. The airplane was substantially damaged and the commercial-rated pilot and one passenger were not injured. One passenger sustained minor injuries. The flight originated about 1800, from Winter Haven's Gilbert Airport, Winter Haven , Florida. The pilot stated that during cruise flight about 700-800 feet msl, while returning to the departure airport, the engine experienced a gradual loss of power. He attempted to correct the loss of power situation but was unable. He did not recall the airspeed but noted that the engine rpm decreased to 2,400, and he was unable to maintain altitude. While descending, the airplane collided with a tree then the ground and nosed over. A postcrash fire destroyed the airplane. Examination of the accident site by an FAA airworthiness inspector revealed that the left wing of the airplane separated after a tree contact. The airplane then impacted the ground approximately 100 feet from where the left wing contacted the tree, and nosed over coming to rest against trees. A post crash fire consumed the fuselage between the firewall and the empennage. The mixture control at the fuel metering valve was found about half way between midrange and idle cutoff, and the mixture control cable was found separated from the rod end which was still attached to the Bellcrank (Mixture) at the airbox assembly. The threaded portion of the mixture cable was examined and damage to the major diameter of the threads for a length of 5/8 inch was noted; consisting of about approximately 11 threads. The diameter of the damaged threads was measured and found to be 5/32 inch. The diameter of the undamaged threads was measured and found to be 6/32 inch. No determination was made as to whether the internal threads of the rod end were damaged. The pilot who was the owner of the airplane reported to the FAA inspector that the maintenance records were inside the airplane at the time of the accident. No records or remnants of records were located in the wreckage. The FAA inspector contacted the mechanic who performed the last annual inspection, and that person advised the FAA that the owner assisted him with the inspection of the airplane and that the owner performed Airworthiness Directive AD 86-24-07 and adjusted the mixture cable rod-end to attain the correct cushion. The mechanic stated that he checked the adjustment but failed to check the jam nut at the rod end. According to FAA records, the pilot is not a certificated airframe and/or powerplant mechanic. The pilot/owner stated that during the last annual inspection, he did whatever "Bob" told him to do. He was in the cockpit and Bob was in the engine compartment. Bob wasn't happy about either the mixture or throttle not going full travel. He stated that he couldn't recall in what direction. He further stated that he did not do any adjustment in the engine compartment, but he was assisting to save on the cost of the annual inspection. He has owned the airplane for about 2 years and during that time, the mixture and throttle cables had not been replaced. When asked he stated that he did not help with the adjustment.