ACCORDING TO A PERSON WHO HELPED ASSEMBLE THE ULTRALIGHT VEHICLE FOR FLT, THE BASE OF THE CLOUDS WERE AT ABOUT 200 FT AGL, WHEN THE PLT TOOK OFF. THE HELPER EXPECTED THE PLT TO RETURN & LAND DUE TO THE WX; HOWEVER, THE VEHICLE CRASHED IN A WOODED AREA. THERE WAS EVIDENCE THAT IT CRASHED WHILE FALLING VERTICALLY IN A WINGS LEVEL ATTITUDE & MOVING REARWARD. FLT CONTROL CONTINUITY WAS VERIFIED & ALL 3 PROP BLADES EXHIBITED ROTATIONAL DAMAGE. THE THROTTLE CONTROL CABLE WAS FOUND DISCONNECTED FROM THE CARBURETOR. THE CARBURETOR WAS DISASSEMBLED & THE CABLE'S SWAGED END FITTING WAS FOUND LYING LOOSE IN THE BODY OF THE CARBURETOR. WITH THE SWAGED END OFF OF THE CABLE, THE ENG WOULD HAVE GONE TO IDLE POWER. NO EVIDENCE WAS FOUND TO SHOW THAT THE CABLE WAS FORCIBLY PULLED LOOSE. APRX 45 MI SOUTH A DALLAS, TX, THE 0748 CDT WX WAS: 300 FT SCATTERED, 900 FT BROKEN, VISIBILITY 6 MI WITH FOG & DRIZZLE, WIND CALM.