Motorcycle Repair: 1981 honda cb900c, honda cb900c, carburetor bodies

Question
on the carbs between#2 and #3 there is a vacuum tube that hooks up somewhere it goes to the barrel slides in the carbs but I cant find where the vacuum comes from the vacuum tube from #2 runs to the inline fuel diaphragm but cannot find where the other vacuum is going to get to the slides

Answer
Mark...

The only vacuum line you have to worry about is the #2 line to the fuel control valve. DO check it to ensure that the diaphragm that it is attached to is not leaking. If the diaphragm fails, you get a vacuum leak at #2 intake runner and a reduction or stoppage of fuel delivered to the carburetor rack.

http://www.cmsnl.com/honda-cb900c-900-custom-1981-usa_model7249/partslist/E++21.

There are three interconnecting lines between the carburetor bodies...
Vent lines...
Fuel lines...
Accelerator pump feed lines...

http://www.cmsnl.com/honda-cb900c-900-custom-1981-usa_model7249/partslist/E++20.

The carburetor slides get their vacuum from passageways inside the carburetor bodies, fed by the intake manifold vacuum signals.

The vent lines just vent to atmosphere, so don't attach to anything.

Bill Silver