Remove the black rubber covering the spark plug. Disconnect the spark plug by pulling off its wire from where it is connected.
Take off the bolts securing the starter shroud with a wrench. Remove the starter shroud. Turn its pulley counterclockwise until it cannot turn any longer, then hold the pulley in place with vice-grip pliers. Untie the knot at the center of the pulley to remove the old pull cord.
Slip the end of a new pull cord into its hole in the starter shroud. Pull in this end and run it into the knot hole inside the pulley.
Tie the end of the cord into a knot. Apply heat from the flames of a lighter to the frayed ends of the knotted cord to singe it. Pull the cord taut to rest the knot against the inside of the knot hole.
Release the vice-grip pliers to let the pulley roll up the new cord. Replace the starter shroud and bolt it down with a wrench. Reconnect the spark plug and replace the black rubber covering it.