if you have type one carbs and the drain screw slots are unusable,youve probably gotten one or two out with self locking pliers,ive even sheared them off with a screw driver before,if they come out and you want to replace them with an easier screw,just use a 1/4 UNF tap and just with some finesse run it through the existing hole and thread,then use stainless button heads with an appropiate o ring under it,dont winch them down too tight,just flatten the o ring then nip it up,,you have to remove the screw fully to get the drain action again,if youve sheared of the factory brass screw,carefully run a 5.5 mm drill bit through it trying to keep it centred,,the bit should track into the drain hole in the brass left over thread,,then run your 1/4 UNF tap through that paying a little more attention on this one to keep it centred.
