CAUTION: Before performing maintenance on any unit, always disconnect and ground the spark plug wire.

The reason this usually occurs is due to the large spring at the back end of the shaft assembly getting rusted or impaired with debris. This assembly has the blade attached to the front of it. This spring can create a bind to the shaft assembly by essentially grabbing the shaft and holding it. By holding the shaft, the spring does not allow for proper head movement and positioning, and therefore causes the depth control handle to jump out of position.

It is necessary to maintain and lubricate this spring liberally with some motor oil from time to time to keep these parts moving freely. The common practice is to clean the dirt from this spring area and then brush some motor oil onto and into the coil spring focusing on the front and back end. This often frees up this assembly and restores full range of motion.