TYPE 60C CARB throttle stop screw
Bob,
Your O.S. Max #60C carb should have no problems allowing you to set the throttle stop screw so that the carb can close enough to shut down the engine. It's possible your stop screw has a broken tip and is jamming in the slot. Take the stop screw out and check the rotor. Also look at the stop screw. It does sound like something's amiss.