The port is on the carburetor but these solex carbs arent exactly like a webber carb, theyre "sPEcIAl" because they have turned my upside down inside out trying to tune and adjust them but i finally got it down after about a year of just these pair of solex carbs, i wish i could upload a file of the pic where the vac port is on these carbs. But these carbs butterflies dont open normally they open opposite ways of each other so like thing of when the throttle is opening the butterflies look like (if it was cut away) pointing down like an arrow facing down, but when theyre closed theyre kind of flat or slightly open for the idle circuit, plus like i said the pushrod of the vac box barely moves when i push on it and i cant get it to activate by simply sucking on it