XS650 BS 34 carbs already have a tee, so I assume that you are asking about adding a tee to a BS38 set-up. It's not necessary. The two BS38 carbs are already connected by a cross-over tube. Run your supply to one inlet, cap off the other inlet, and you're done. You'll find that this is a lot easier than trying to figure out where to put a tee and how to route two lines.