The way I do it is probably not the best but it works for me.
cut your rope to length and tie a knot in the end.
with the fuel tank off turn the rope spool clockwise about 6 times and around until the hole in the middle where the rope goes through is close to the part where the rope comes out. Hold in place.
Feed the rope (end without the knot first) in the middle of the spool and out the side to where the starter knob usually sits.
as you are nearing the end of the rope attach the knob on the end.
There is probably a better way but it is fairly quick and simple.
