Most self propelled tools use a fan belt and pulleys. When you engage it it just tightens up the belt so the pulleys take up the slack in the belt and it turns the pulleys. Sounds like it just needs to either be adjusted or worst case a new fan belt. I know my snowblower has a fold down handle that loosens up the cables. When unfolded the cables tighten up. There are a series of holes for that cable to plug into on that cam to take up the slack on the cable I would image to allow for wear and the belt stretching. How about just flipping the machine over and looking at how the works and take off your Pink Square Snowflake Hat and putting on a Thinking cap and work the problem people. Not guessing and making the problem worse!