The starter rope on a Stihl chainsaw, combined with the pulley and recoil spring, turn the flywheel fast enough to fire off a spark in the chamber. This action needs to happen at the right moment or the chainsaw will not start. Over time, the starter rope will wear out, get frayed or break from excessive pulling, and you will need to replace it. You may also get pitch on the rope causing it to stick and jam up, in which case you will need to replace it as well.
Remove the four screws retaining the fan housing with the screwdriver. Lift the base of the fan housing and pull it off the housing area. Wedge the tip of the screwdriver underneath the spring clip that's connected to the starter post. Pop the clip off gently.
Slide the washer and pawl off the starter post. Pop the cap off the top of the starter handle. Push the knotted end of the rope through the starter handle, making sure not to remove the sleeve inside the handle as well. Remove the rope rotor or pulley from the starter post.
Pull off any old starter rope. Cut the knot off of both ends and throw the old rope away. Tie an overhand knot into the end of the new starter rope. Feed the rope through the hole on the rope rotor and pull it all the way through. Thread the rope through the hole on the fan housing cover and the base of the starter handle.
Leave about 3 inches remaining out the end of the starter handle. Tie another overhand knot into the end. Pull the knot down into the handle and refit the cap in place over it. Lubricate the starter post with the engine grease.
Twist the rope rotor back and forth until it connects to the recoil spring. Push the rope rotor back onto the starter post. Refit the pawl and washer on top of the rope rotor. Connect the clip back on top of them, making sure it is pointed clockwise.
Tension the rewind spring by making a loop in the unwound starter rope between the rope rotor and the top of the fan housing cover. Hold the loop and turn it six full revolutions clockwise. Hold the rotor steady while you free the loop and untwist the rope.
Let go of the rotor and let it wind the rope onto the pulley; it should hold the starter handle firmly against the cover and not droop. If it droops, repeat the tensioning step and add one more full revolution.
The spring is under high amounts of tension and can pop out unexpectedly, causing serious injury.