The picture below indicates the metalic coil stop at the end of each coil (I'm resting my fingers on the coil stop). This part sometimes gets beaten out flat with repeated use, or one of the screws can fall off leaving the coil rather loose. You can jiggle each coil around and see if it feels loose or not. If so, you may want to release the coil stop by backing off the screws, reposition it, and then tighten the two screws back down.
(click any picture to enlarge)