So I swapped a perfectly working '71 TQ and the problem persists. I'm getting about 9-10" vacuum with both carbs and I tried several base gaskets. After everything, the leak is coming from under the intake or what? Bad valves?? I'm going to perform a leak down and compression test once the engine cools. I'm dreading removing the manifold as the car has AC and it looks like I have to remove the compressor to get to the hoses and front manifold bolts. The system is charged so I guess I'm going to need to have it evacuated too. Sucks.