Find the blade drive belt, and you'll find that a tensioner wheel that pulls the belt tight is not doing do when you engage the cutting drive lever because of the errant spring....often you can see where the spring goes if you can find two drilled holes where the spring connects - one hole will be on the tensioner wheel itself (not the revolving part, obviously) and the other will be on the metalwork nearby. Look for areas where the paint has rubbed off due to the spring movement.
John, March 2008
