Hi, I have just had to work this out too.
Try and follow this, I think it's how it's done:
*Remove the bump knob and spool.
*On the internal spool on the top you will see an arrow pointing one way and oppopsite it, another arrow pointing in the other direction.
Look at the inside centre of the spool and you will see two holes, one on each side of the spool.
*Cut 2m(ish) of line, then cut in half so you have two equal lengths
*Insert an end of one of the pieces of line into one of the holes and wind it onto spool the same direction as the arrow shows. when you are near end of the line(so to speak), lock into one of the little slots in the spool so it won't unwind again
*repeat this with the other length of line in the other hole wind it in the other direction as indicated by the arrow, finishing it in one of the slots which is opposite the first one.
*insert the line through the holes in the outer spool and reassemble it all.
*Pull the cord through the holes so they come out of the locking slots
*You should (hopefully) be ready to toil away in the hot sun!!!
Good Luck
Ron, January 2008