THE PILOT SELECTED 25 DEGREES OF FLAPS AND TOOK OFF ON RUNWAY 26L FROM INTERSECTION B5 (4465 FEET OF RUNWAY AVAILABLE, 10,004 FEET TOTAL LENGTH). HE SAID THE AIRPLANE CLIMBED TO ABOUT 300 FEET AGL, THEN THE STALL WARNING HORN SOUNDED. WHEN HE LOWERED THE NOSE TO INCREASE AIRSPEED, THE AIRPLANE DESCENDED. WHEN HE RAISED THE NOSE TO CHECK THE DESCENT, THE STALL WARNING HORN AGAIN SOUNDED. THIS SITUATION CONTINUED UNTIL THE PILOT WAS FORCED TO MAKE A CONTROLLED CRASH INTO A TREE IN A RESIDENTIAL NEIGHBORHOOD. DENSITY ALTITUDE WAS COMPUTED TO BE 7181 FEET. THE WINDS WERE FROM 010 DEGREES AT 21 KNOTS, GUSTING TO 30 KNOTS. REPORTEDLY, THE PILOT ENRICHED THE MIXTURE BEFORE TAKING OFF, THEN CONFIRMED THE THROTTLE AND MIXTURE WERE 'FULLY OPEN' AFTER THE STALL WARNING HORN SOUNDED. HE NOTED THAT THE TACHOMETER FOR THE FIXED PITCH PROPELLER WAS INDICATING 2400 RPM AT MAXIMUM POWER.