[Pete]

Dave, per Jac Mac's post, loosen the three screws that hold the bimetal spring cover. You should be able to rotate the cap in either direction. Sometimes one of the screws has a set of teeth that might restrict movement. Simply take the teeth off. Now, rotate the cap clockwise to open. To set the butterfly to the best setting rotate the cap counterclockwise to the closed position. Only you don't want the butterfly closed tight against the airhorn. You want the butterfly to be closed so that you can push it open with very light pressure with your finger and it springs back to the closed position leaving about a 1/16 to an 1/8 gap. Now tighten the screws and that would be a good setting. sometimes the bimetal springs don't jive with the marks, or as the spring ages the marks will be off. Now when the engine warms up you should be able to tap the throttle lightly and it will kick off of fast idle. Hope this helps.
Pete