There will be two screws, one that sets the idle speed by bearing against the moveable throttle lever, and another one that screws into the carburetor base with a tension spring under it to keep its setting. This is the one you need to open up (counterclockwise). It controls the volume of gas vapor and air that enters the engine at idle by moving a tapered point into a hole in the carburetor housing. Opening up the passageway allows the gasoline to flush out any debris which is clogging the passageway, hopefully. If the procedure clears up the stall at idle, just turn the screw back to its original position and drive on. If not, it's time for a carb rebuild, and your rebuilder will readjust the idle speed and mixture as part of the reinstallation process.
Jerry
