How to test a vacuum operated petcock

[zuzu]

I just ordered a Petcock for my 82 GS1100E from z1enterprise. They where very helpful and had the best prices and shipping that I could find. Here is there link http://www.z1enterprises.com/
Hope this helps.

Tony

[Billy Ricks]

I am stupidly baffled about this because it doesn't make sence that there is a fuel pump that is under the tank on the opposite side of the frame tunnel, but I don't know what it is since I'm also pretty sure it isn't a sending unit????

What connects to this nipple and why???

It is the sending unit for the gas gauge. It will have two wires coming out of the cover with the nipple. Usually a drain line is connected to the nipple and routed to the back of the engine in case a fuel leak develops from the float assembly underneath.