My secondary butterflies on my 77 K20 pickup Qjet are sticking slightly right off fully closed. Bumping them with my finger seems to close them just fine. A little wear (bright spot) from the secondary plate can be seen right where the butterfly is contacting the air horn and binding. The truck runs but I'm trying to maximize economy. Do I need a new air horn or is there a way to correct this one? Thanks for the help!