Vent or Vacuum?

1976 KZ900, 1015 block. Here's a realy dumb question.

I have replaced my 26's with 28's but I got the 28's on E-bay and do not know from what year they are. I THINK they are 1975? they have the sync adjustment screws on the outside of the carb body, utilizing a way more complicated slide lifting system than seems necessary. They have air screws not fuel mix screws.

My question is.....Are the two upper spigots purely vents or are they vacuum tube fittings which should go back to the tank? If they ARE vacuum fittings but I am using a single spigot (non-vacuum) petcock, what should I be doing with the tubes I connect to these spigots. Use a "U" tube and connect one spigot with the other?

Thanks.

I think they are vents, the spigots that are for a vacuum actuated petcock go all the way into the carb venturi and are easy to see from the motor side of the carbs if you look into them. you will see the brass fitting on the top/side (inside the carb). have a look on wiredgeorges website under the "carb connections" section
Scott

Yup, took a look at them last night, they are vents, not vacuum. Thanks.