You should check the bushings in the driven sheive it should be nice and tight side to side but turn on the shaft easily as it has to turn back and forth for the cam to be able to tighten the belt as it is working the heavier spring only puts a partial tightening on the belt . Also there is a small radial bearing under the spring that allows the spring to turn as the speed changes which tends to get rusted up and won't turn easily this all helps out the torque sensing of the pulleys work , as the rotor needs more torque the driven pulley will tighten itself up on the belt through the cam assembly . they should all move easily and not bind anywhere .