need heip...HAVE 2 DIFFERENT HEADS WITH THIS MODEL. TB 80 EC : ONE IS A NORMAL HEAD THAT YOU WIND THE STRING AROUND, BUT THE OTHER HAS IT WHERE YOU JUST PUT A LENGH OF STRING IN IT. AND IT IS NOT A BUMP HEAD AS THE OTHER ONE IS. PROBLEM IS THAT WE DON'T KNOW HOW TO THREAD THE LENGH OF STRING INTO HEAD AS WE GOT NO MANUAL OR DIRECTION WITH THIS WEEDEATER...COULD YOU PLEASE HELP AS WE NEED TO USE IT ASAP!!!!! THANKS