Rebuilding a recoil starter without losing a finger or the spring

Take the housing off, pull the rope out fully and tie a slip knot so the pulley stays wound, cut the old rope at the handle. Let the pulley unwind slowly against your thumb to count the turns. The spring is under the pulley: leave it in the housing if it is not broken. New rope: same diameter (#4 or #5 usually), melt the ends, feed through, knot. Pre-tension by winding the pulley 4 to 6 turns before threading the rope through the housing hole. Test: the handle should retract fully with a little tension left.

If the spring is broken, buy the whole pulley-and-spring assembly for $12. A loose recoil spring is a sixty-mile-an-hour slinky.