Try, if you can, not to undo the recoil mechanism if at all possible, as there is a huge spring that will leap straight over the garden wall....its usually possible to thread the new starter rope into the plastic pulley, and then tension it by winding the rope around the pulley, courtesy of the small notch that allows the rope to pass round it....much easier said than done and even harder to write about! A garden machine shop will do it for you for less than a tenner.
John, June 2009