Whether the pull cord on your Poulan weed eater is broken, worn out or not pulling in and out correctly, you will be faced with changing this cord. This cord is critical for getting your trimmer started, so you should always make sure it's working properly. The starter cord sits on a pulley that's tightened by a recoil spring inside that pulley. If either of these parts is broken you will need to replace them as well.
Use the screwdriver to remove the starter cover screws. The starter cover on most Poulan models is at the back end of the engine, near the muffler. Take off the starter cover and the starter cord should come off with it, because it's attached to the starter cover.
Pull out the entire length of starter cord from the pulley. Locate the tab in the pulley's center that locks this cord in place. Pop this up with your finger or the screwdriver. Pull the cord off of the pulley.
Use the screwdriver to open up the plastic starter handle off of the old cord. Untie the rope from the metal insert that's inside the handle. Discard the old cord.
Insert the new cord into the same center access hole that you pulled the old cord out of. Pull it all the way through and lock the center tab by pushing it down into place over the new cord.
Thread the new cord through the metal insert and the plastic handle. Tie a regular, overhand knot in the end, but keep the knot loose. Push the knot inside the handle, tighten it against the metal insert and close the handle over the knot and metal insert.
Wind the cord around the pulley all the way. Hold the cover in one hand and pull out the cord two full pulley rotations to set the tension on the recoil spring. Repeat if necessary to get the proper tension on the cord. Screw the starter cover back into place over the engine.
Don't let the recoil spring come off of the pulley when you pull out the old starter cord. If this happens you will need to push this spring back in, which can be very tricky.