Check the black plastic catch inside. If it is broken replace. The double prongs go in the circular hole and the single point moves freely in the square hole. Both ends of the spring are on the outer side of the gold receptacle. To ensure long pullstarter life prime the engine before starting, use the choke lever on the first pull, pull rope gently until you feel resistance, then start.
Screws are loose.
Due to the vibration of the motor screws can easily come loose. Common ones are on the pullstarter, motor mount, intake manifold, and gas tank. Check these screws carefully every week or so. Locktite can be used on them but will make removal difficult. When replacing screws make sure metric threads are used.