I've never encountered this before...the top right port (about 1/4" round) is usually where I find full vacuum at idle. This carb has NONE coming from it. I'm concerned it is causing it to run poorly...and I don't have a known good carb to swap and test. Prior to running the car, I pulled the carb apart and cleaned it up really well...and installed new gaskets. They were exactly the same as the ones that came out of it. It's a 72 Stage1 carb on a 455 that sounds like it has a bit of a choppy cam...but nothing huge. There was no spec provided with the car, so it's all a guessing game at this point on what has been done to it. Supposedly Rick Henderson built the engine, so he may know. I don't know how to get a hold of him anymore.