Turn the Poulan weed trimmer off and place it on a flat surface like a table or workbench. Let the tool cool off completely to avoid burns.
Insert a screwdriver into the bottom screw of the flex shaft near the black round knob. Turn the screw counterclockwise to loosen it and pull it straight out. Pull the flex shaft out of the lower shaft.
Place a pair of adjustable pliers on the bolt in the handle and hold it in position. Turn the wing nut on the bolt counterclockwise to loosen it. Remove the bolt and wing nut from the handle and set them aside. Pull the handle straight off the flex shaft and set it aside.
Insert a screwdriver into the screw in the throttle control assembly. Turn the screw counterclockwise to loosen and remove it. Repeat this process to remove the additional three screws. Pull the front half of the throttle control assembly off by lifting it straight up. Pull the flex shaft down and out of the bottom half of the throttle control assembly.
Place a new flex shaft in the bottom half of the throttle control assembly. Do not disturb the throttle cable wire or switch in the bottom.
Place the top half of the throttle control assembly on top of the flex shaft, insert the four screws and tighten them clockwise.
Align the bolthole in the handle on the flex shaft. Insert the bolt, hold it with adjustable pliers and tighten the wing nut clockwise on the bolt.
Insert the bottom of the flex shaft into the lower shaft, replace the screw and turn it clockwise to tighten it.