If you look close at the previous pics the diaphram vent is on top at the back. Air could blow over it, but not directly into it. Look at these pics, they are a little fuzzy. Got too close with the camera. With the rotater manifold I built the needles and idle adjustment are pointing up and the diaphram vent is on the back and bottom, though you can't see it.
It picked up a 100 rpm with the straight in manifold as opposed to the original angled one. 6800. Bambula 20x8. Put on a muffler and might have lost 25 to 50 rpm. Then tried a APC 20x10. Pulled 6400 rpm. The carb just started to need a little leaning out on the low side when I quit. Engine has a ways to go to settle in yet. Hope it picks up some then.