THE PILOT'S FAILURE TO MAINTAIN ADEQUATE AIRSPEED DURING A TAKEOFF WITH LESS THAN FULL POWER RESULTING IN A STALL. CONTRIBUTING FACTORS WERE THE PILOT'S FAILURE TO LEAN THE MIXTURE TO COMPENSATE FOR THE HIGH DENSITY ALTITUDE, AND THE GROSS IMPROPER, INADEQUATE MAINTENANCE THAT HAD BEEN PERFORMED ON THE ENGINE RESULTING IN AN UNAIRWORTHY ENGINE.