Repairs Hard Shifting on Craftsman Rider

I have a 1995 Craftsman Rider (model: 917.257644). When the engine is off the shifter works normally, but when the engine is running the gear shift is very hard to move between gears. I am guessing that the clutch isn't fully disengaging the belt and that the continued motion of the pulley is the problem, but i don't see any obvious adjustments in the clutch / idler pulley system. Will a new belt do the trick? Looking for ideas. Thanks!

Repairs Hard Shifting on Craftsman Rider