This is not an easy task but doable with two people. Undo the toggle (i.e. pulling mechanism) and detach it from the the yellow outer housing. This seems counterintuitive but makes sense in the end.
Simply rewind the spring around the White spindle. Rewind quite tightly and hold on tight and do not allow it to unravel or twist. Then use a strong elastic band and tightly hold the wound spring in place against the white spindle. Then place the hooked end of the spring in its retainer by inverting the spindle and turning. Make sure that it is firmly in place and screw the allen key bolt in the centre until virtually full tight. Cut the elastic band strings while pushing down on the spindle, lift very slightly to allow the cut ends to be pulled out. Once all out then fully tighten. My wife and I managed to do this in about 5 minutes. It takes co-ordination and determination, but it is doable and has saved us from buying anything new. The chain saw now works perfectly..
Adrian Conway-Hyde
January 2012