On the 1983 YTM200 intake boot between the carb and the head there is a nipple for a hose. Is this a vacuum line? If so where is it supposed to be hooked to at the other end? the guy who had it before me had a vacuum line on it with a screw in it. Why would Yamaha put a vacuum line on a bike just for you to plug it with a screw? Any help would be appreciated.