Here's a picture of the APT with the black plastic spacer (in place of the aneroid). You can also see the metering rod. There's a spring loaded screw on top that changes the pressure on the metering rod, thereby changing the depth of the metering rod in the APT metering jet. From what I can tell, there's no vacuum that's applied to this setup, it's just a carry-over from when the aneroid changed the rod height. I can't see how the black plastic spacer helps the situation. That's why I'm wondering if I should just plug the APT jet.