Re: Mysterious "t-piece" between carbs on '81 CB750K...

Posted by seestheday on Jan 28, 2012; 1:12pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Mysterious-t-piece-between-carbs-on-81-CB750K-tp3691494p3695761.html

I believe its used as a part of the auto petcock.  I recently removed my autopetcock and my bike runs much better.
If you have removed it you can leave it open or stick a hose on it and run it into the airbox or put a little filter on it if you want.  I'm running mine open and haven't had any issues.
I think stock was actually just a hose running to the airbox.

Don't cap it.  There is another port that should be capped without the autopetcock on the front of the carb block between carbs 1 and 2, kind of on the opposite side of the fuel port.

I have the same bike as you.  Enjoy!