On September 29, 1998, at 1620 central daylight time, a Beech 35, N8946M, piloted by a private pilot, received substantial damage on impact with terrain while returning to Runway 29 (3,730 feet by 100 feet, asphalt/dry) at M. Graham Clark Airport (PLK), Point Lookout, Missouri. The aircraft experienced a partial loss of engine power. Visual meteorological conditions prevailed at the time of the accident. The pilot and passengers reported no injuries. The 14 CFR Part 91 personal flight was not operating on a flight plan. The flight departed PLK, at 1620, and was en route to Slidell, Louisiana. The pilot reported that during his initial departure at 1400, there was a high exhaust gas temperature (EGT) indication. The pilot then returned to PLK where a mechanic looked at the mixture control. The pilot stated that during a second departure attempt, the aircraft would not continue to climb after the gear was retracted at an altitude of approximately 100 feet. He further stated that the engine apparently continued to decrease in power output and that he maintained a low downwind to Runway 29, turned to line up with the runway, and impacted the tarmac. The Airport Operations Manager reported that he saw the aircraft with its landing gear in the down position and that he had heard the engine running very rough. He also noted that the aircraft was banking steeply trying to turn to the centerline of the runway. He further reported that the aircraft's left wing struck the gravel on the south side of the runway, the right main gear broke free and, the nose gear folded up. He added that the aircraft slid towards the centerline of the runway and came to rest approximately 300 feet after its initial impact point which was located approximately 450 feet beyond the threshold of Runway 29. The Airport Manager also stated that the nose of the aircraft was orientated 30 - 40 degrees right of the runway's centerline. The pilot reported that the mechanic, who inspected the mixture control, had replaced the outer mixture control clamps. The pilot also stated that the mechanic recommended to leave the control full rich until a mechanic could troubleshoot the reason that the control linkage allowed the mixture to go over center. The pilot stated that no paperwork was done on the clamp replacement and that the mechanic did not want to charge for the work. The mechanic stated that he was told that the pilot could not shut down the engine with the mixture control, and that the pilot had to use the key. The mechanic stated that he was not told about the attempted departure, or that the pilot had noted a high EGT and had experienced a "partial power loss". The mechanic stated, that he had replaced a cable housing clamp and rigged the mixture control to the full rich stop. He also told the pilot that it was still not rigged correctly and would take a week to troubleshoot and repair. The mechanic further reported, that he showed the discrepancy to the pilot and told him he could do whatever he wanted to do. The mechanic stated that he did not make a logbook entry and did not issue a work order. Inspection of the aircraft by a Federal Aviation Inspector revealed that there was fuel present in both fuel tanks. Both magnetos were tested and no anomalies were noted. Inspection of the mixture control revealed that it was not travelling to the idle cut-off stop and that the full rich stop pin was not in place.