Sorry this took so long to get to...am changing isp etc.... I would suggest you check out the carbs very closley as it has to be there somewhere....use a small torch...like CSI. You may find it has an old pipe already attached making it harder to find. Take off the tank if you havn't already done this.

Good luck

Seems you're the guy to ask. Recently bought 79 gs550, basically a bucket of rust, but running. I can't figure out where the fuel cock plugs vacuum line plugs into (the back side of the fuel cock that has the diaphram). I can't find anything on the carbs (where my other bike (vulcan 500 0 plugs into) where to plug it in. Any help is appreciated.