This is a 2v carb autolite assume 2100. On the back of carb at base there is a rubber deal (looks like miniature off road shock boot) sticks out and has a screw with a domed metal washer and a rubber washer. This is vaccum for something it falls off freely and really makes engine run bad. I was told this is for the vaccum if you have power brakes. I assume this should be plugged off.