AFTER MAKING A TOUCH-&-GO LANDING, THE PLT BEGAN A TAKEOFF WITH 10 DEG OF FLAPS. THE FLT MANUAL RCMDD TAKEOFFS BE MADE WITH THE FLAPS FULLY RETRACTED, EXCEPT FOR SHORT FIELD TAKEOFFS OR TAKEOFFS ON SOFT OR ROUGH FIELDS WITH NO OBSTACLES AHEAD. THE PLT STATED THAT AFTER CLIMBING TO ABOUT 300' AGL, HE NOTED THE ACFT WAS NOT CLIMBING PROPERLY & THAT THE ENG DID NOT SEEM TO BE PROVIDING FULL POWER. HE DID NOT CHECK THE ENG INSTRUMENTS TO VERIFY THE ENG PERFORMANCE. HE LOWERED THE NOSE TO ACCELERATE & STARTED A RIGHT TURN TO AVOID AN OBSTACLE. AT ABOUT THAT TIME, THE ACFT STALLED, THEN CRASHED BEFORE THE PILOT COULD RECOVER FROM A DESCENT. THERE WAS EVIDENCE THE ENG WAS DEVELOPING POWER AT IMPACT. A TEARDOWN OF THE ENG REVEALED NO EVIDENCE OF A PART FAILURE OR MALFUNCTION. DENSITY ALTITUDE AT THE ARPT WAS APRX 6500'.