yes, that's what I've been saying all along in this thread.OK thanks. So you're saying when synching the carbs, you pull the hose off the petcock and use that? That's not how I did it when I last synched my carbs - there are two plugged hoses on the right side and the two connected to the T on the left side.
here's the service manual page that confirms it
that's the only hose connected to the #3 cylinder, so if the petcock is permanently removed, that's the line that you must plug. It sounds like you've done that, so you've done everything that needs to be done.
Regarding a possible vacuum leak, any chance that one of your 4 plugged vacuum lines has either a split in the hose, or a leak in the plug?