I appreciate all the help on this. This is what I have found out. On the ST that I have, the idle stop screw that comes down on the top side of the carb is really not needed since the radio equipment that we are using these days will control the idle and stopping of the engine reliably. With the screw out, the barrel will not move laterally because there is a horizontal screw that is in place coming into the side of the carb to keep the barrel in place. I flew the plane today without the screw in place, the motor ran perfectly for four, seven minute flights. It was a good day. Thanks everyone for your input.