The starter spring on a McCulloch string trimmer rides on the inside of the recoil pulley. This spring attaches to the pull rope so when you withdraw the rope, the spring automatically retracts the rope when you let go. This spring can be damaged from pulling on the rope too hard or it can just wear out over time. Regardless, without this spring working properly, you will not be able to start your McCulloch string trimmer's engine.
Undo the two screws holding the throttle cover in place over the throttle trigger, which are next to the trigger. Undo the screw on the side of the trigger and remove the trigger cover and trigger. Loosen the throttle wire's bolt and disconnect the throttle wire from the throttle trigger.
Undo the top screw that sits just above the throttle's protective sleeve. Separate the shaft from the rest of the engine by gently pulling it away from the body.
Undo the four screws holding the starter housing in place on the engine. Remove the starter housing cover. Some McCulloch trimmers may have an additional four screws holding the housing cover to the frame of the engine; remove them also.
Pull the housing cover away from the engine. Undo the recoil pulley and starter spring's retaining screw, which is on the underside of the pulley. Remove the pulley and starter spring from the housing cover.
Withdraw about eight inches of rope from off the pulley. Twist the rope into a loop. Pinch and hold the loop in your fingers where the two ropes cross. Hold the pulley in your other hand and rotate the loop back and forth to free the spring from the rope.
Pull the old starter spring from the recoil pulley using your thumbnail. Push the new starter spring into the centre of the recoil pulley. Form the same loop in the rope and repeat the process to reset the tension on the rope.
Screw the recoil pulley and starter spring back to the starter housing cover. Set the housing cover back in place over the engine. Tighten the cover's four retaining screws with the screwdriver. Connect the shaft to the engine and tighten the shaft's locking screw.
Reconnect the throttle wire to the throttle trigger. Reassemble the trigger sleeve cover and throttle cover and tighten its two screws.