The vacuum ports on the carbs that I show in my BS series carb connect document on my web site are typically capped with 7/32" vacuum caps because many owners have removed the emissions equipment from their bikes. On MOST emission equipped bikes, the #2 vacuum port is connected to the petcock via a hose. It is very important that this hose not be cracked and not leak. Leaks ANYWHERE in the carb system create too much air and upset the air/fuel mixture; especially the idle and if a hose like this leaks, the bike won't idle at the proper speed. I generally cap the other vacuum ports but on a STOCK bike WITH emissions equipment, #3 will be capped from the factory and #1 and #4 will have hoses connected with go to a tee. From there tee there will be a hose to a vacuum switch which actuates the reed valves which are up in your valve cover. The reed valves are covered by plates which have a hose joining them with a tee in the center. This is a large diameter hose; about 1". The hose goes back to the airbox. This is to route unburned crud that escapes when the reed valves are open to your air filter where in theory, it is sucked into the intake and burned. The unburned stuff comes from incomplete combustion... the reed valves are atop 1/2" holes in the cylinder which sit over your combustion chambers. The holes come out right by the exhaust vavles. When vacuum from the carbs actuates the mechanism that opens the reed valves, these guys pop open and unburned crud swirls around the bike and ends up supposedly being burned again. In practice, most owners just remove the BIG 1" hoses, the actuating can where the vacuum is hooked and the hoses leading to it and just plug 1&4 vacuum ports. You also have to plug (use Black Permatex) the snouts where the big hoses were connected above the reed valves. Leave the reed valves in place as they have rubber sealing gaskets unless you buy "block-off plates" from a company like APE who makes some pretty billet covers. If you don't and the bike hiccups, the reed valves could otherwise blow open and the combustion chambers would be momentarily open to the air through the unblocked snouts and flames WILL come out the snouts. Since they are under your gas tank and coils I suspect it is better to put some Permatex in the snouts.