First thing would be to check it for cracks or worse missing chunks out of it. Since it sounds like you have a gear drive I would with the engine off put it in gear and let out the clutch. Then take hold of the belt and see how tight it is and if it can be slid on the pulleys any at all. If it looks OK but seems loose there normally is a way to adjust it by changing the tension on the clutch idler pulley.How do I check belt? What do I need to do to tighten it?