The pull cord on a Troy-Bilt TB20Cs operates the starter mechanism on the engine. This cord spins the flywheel, which turns the crankshaft and ignites the spark. Sitting at the front end, near the shaft handle, the pull cord on this model is accessed through the front, requiring you to remove the clutch. The pull cord may break if you pull it out too hard; it may also come loose of the recoil spring, or it may no longer retract.
Unscrew the rear shaft grip from the unit. Unscrew the attachment bolts at the boom shaft and power head. Pull the boom shaft away from the power head slowly, as to not rip the ignition cables.
Disconnect the lead ignition wires from the "ON/OFF" switch. Disconnect the throttle wire from the trigger using needle nosed pliers. Pull the shaft entirely out of the head housing area.
Unscrew the mounting bolts of the clutch housing cover. Pull the cover away slowly and disconnect the two ignition switch wires running to the ignition module. Unhook the rubber boot off the spark plug on the underside of the engine. Unscrew the spark plug and take it out of the cylinder with the socket wrench.
Unscrew the clutch drum's mounting bolt with the socket wrench. Slide the clutch drum off the rotor post. Tap out lightly the clutch rotor plate with the hammer and soft drift. Take the clutch rotor off.
Unscrew all of the screws holding the cover to the starter area. Pull the cover off slowly and turn it over to work on the pull cord. Unscrew the pulley from the starter cover and take it off.
Cut the pull cord just underneath the handle and at the knot in the base of the pulley. Take the pull cord off the pulley. Slide the recoil spring out of the pulley and check that it's not bent or damaged; replace the recoil spring, if necessary. Clean the pulley with the rag.
Thread the new length of pull cord through the center of the pulley. Pull it through the hole in the cover and the hole in the handle. Tie a knot at the top, above the handle, and at the bottom, below the pulley. Wind the cord around the pulley clockwise. Fit the recoil spring back into the center of the pulley.
Apply a small coating of engine grease to the starter post on the starter cover. Slide the pulley back onto the starter post and tighten the screw. Pull 10 inches of rope off the pulley and twist it into a loop. Turn the loop back and forth while holding the starter cover to connect the pulley to the recoil spring.
Continue holding the loop while turning the pulley three to five clockwise turns to put tension on the recoil spring. Let go of the loop while holding the cover, and the cord should fully retract. Repeat the tensioning process and add one extra turn if the cord doesn't retract fully. Reassemble and tighten all other parts in reverse order.