THE NEW HOME-BUILT ACFT HAD NO PREVIOUS FLT TIME. AFTER MAKING PREPARATIONS, THE PLT TAXIED TO RWY 33 FOR HIGH SPEED TAXI RUNS WITH RUNWAY LIFT-OFFS. ON THE FIRST HIGH SPEED RUN, HE LIFTED OFF TO ABOUT 20 FT AGL, THEN LANDED BACK ON THE RWY. HE REPORTED THAT ON THE SECOND RUN, THE ACFT LIFTED OFF AND IMMEDIATELY WENT UP TO APRX 40 FT AFTER POSSIBLY ENCOUNTERING A GUST OF WIND. TURBULENCE WAS MUCH MORE NOTICEABLE THAN ON THE FIRST LIFT-OFF. THE PLT BECAME CONCERNED THAT THERE WOULD BE INSUFFICIENT RWY REMAINING TO LAND, SO HE ELECTED TO CONTINUE TO CLIMB. AT APRX 60 FT AGL, THE ENG BEGAN VIBRATING AND THE POWER DROPPED TO ABOUT 2400 RPM. THE PLT ATTEMPTED A LEFT TURN BACK TO THE RWY. HOWEVER, THE ACFT IMMEDIATELY LOST ALTITUDE AND IMPACTED THE GROUND IN A NOSE DOWN ATTITUDE. THE IMPACT POINT WAS IN A SWAMPY THICKET ABOUT 50 YDS FROM THE SIDE OF THE RWY. THE WIND WAS REPORTED TO BE FROM 360 DEG AT 10 GUSTING 20 KTS.