[matt1190]

Well, the port on the back of the carb is for the pcv system. The port in the front gets constant vacuum and is generally not the place to hook up your advance. The port on the metering plate (passenger side) only sees a vacuum when the car is under load. This is the port you want to use for your distributor. Plug the front one. And like PKRWUD mentioned,..you might also have a blown powervalve, but try switching ports first. good luck.