OK. I HAVE A 1981 50HP #6011979. I have a book on it. All has gone well so far. But looking at the throat of the bottom carb at about the two o clock position there is supposed to be a brass screw (which is on the top carb) its not there. The screw is slotted for a standard screwdriver with threads in the center. I have looked at the book several times and cannot find a reference to it. From the looks of the illustrations of the book there are supposeed to be "screens" over the inlate of the carbs. I don't have them on either carb. Is this screw a place to mount these screens? If so are the screens mandatory for the carbs?