THE PLT TOOK OFF ON THE 13,373 FOOT RWY IN IMC CONDITIONS ON AN IFR FLT PLAN. THE ARPT CONTROL TWR CONTROLLER OBSERVED THE ACFT AT MIDFIELD AFTER TAKEOFF, EMITTING BLACK SMOKE AND INFORMED THE PLT. THE PLT REQUESTED AND WAS CLEARED FOR LANDING. THE ACFT WAS OBSERVED IN A LEFT TURN UNTIL VISUAL CONTACT WAS LOST IN CONDITIONS OF LOW CEILING AND VIS. ATTEMPTS TO CONTACT THE ACFT BY RADIO WERE UNSUCCESSFUL. THE ACFT WRECKAGE WAS LOCATED ON TOP OF AN ACFT HANGAR LOCATED ONE QUARTER MILE NORTH OF THE RWY. POST ACCIDENT INSPECTION OF THE ENG AND ACFT REVEALED THE PISTON CROWNS, CYLINDER HEADS, INTAKE VALVES AND SPARK PLUGS WERE COVERED WITH BLACK SOOT. THE MIXTURE CONTROL WAS IN THE FULL RICH POSITION AND THE AUX FUEL PUMP WAS ON. THE ACFT OPERATOR HANDBOOK REQUIRES THE AUX FUEL BOOST PUMP BE 'OFF' AND THE MIXTURE ADJUSTED TO LESS THAN 186 POUNDS PER HOUR FUEL FLOW DURING INITIAL TAKEOFF ROLL.