I don't think the Silver Series 6.5hp Duraforce has an idler pulley, unless that's what I'm calling the 'drive' pulley but I'll double check. All I see (with the cover off) is one pulley with the belt on it. When you let go of the handle the drive mechanism 'tilt's forward which creates all the slack which causes the belt to jump off the pulley. I try to keep the handle pulled in just a bit so as to reduce the slack but it's cumbersome to do that. I'm hoping I can somehow pull the cable tighter up at the handle end and that will keep the slack off w/o engaging it. The spring nor the cable has any adjustability that I see either. Hopefully I'd only have to take off the blade to put on a new belt.