This is a 750 brawler. The picture shows the relationship between the ported vacuum signal hole and the throttle plate. The view is from the top of the carb looking down. The port for the source of lies directly above the throttle plate. Think of the throttle plate as a door blocking manifold vacuum from reaching the port to the ported vacuum circuit. As soon as the door is cracked open it exposes the port to manifold vacuum. From that point as the throttle plates are opened ported vacuum is manifold vacuum. They are the same thing once the door is cracked open. I think the name "ported vacuum" throws people off. It should be call "manifold vacuum that switches off at idle".
Disclaimer. Don't take my word for anything. Go to Harbor freight get a couple vacuum gauges and go for a ride. You can sell the extra gauge to a buddy when your done. Please share your results.
View attachment 1716204388
View attachment 1716204389