On the Juki 98Q, 2000 and 2010 hopping feet, when they sit unused for a while, the oil on the spring gums-up. What we do is spray the spring area of the foot with WD-40, then work the spring until it moves freely. DO NOT push on the bottom circle of the foot, it will break off. Squeeze the spring by placing one finger below the spring, and the other fingernail above the spring in the crack. When it's moving freely, remove the WD-40 with a flannel rag and a can of air. The presser foot tension should be set at near zero, when doing free-motion.