Make sure your gauges are not on a ported vacuum port, look for a port under or even with the throttle blades. You won't gain any information from two gauges as the vacuum will read the same no matter how you adjust the carbs.
You need a air flow meter like the Uni-syn as linked above. They check air flow through the carbs which is set by throttle opening.
Its a simple gauge that blocks the airflow just enough to create a vacuum in the attached tube. In this tube is a small ball. To use the gauge just set on the first carb and adjust it till the ball is 1/2 way up the tube gauge, then with out moving the adjustment set it on the second carb. Adjust the throttle till it reads the same as the first carb. It takes a few back and forth adjustments till you get the just right and get the idle speed just right. Unhook the linkage before starting and recheck after you rehook the linkage. Once set, don't turn the idle screws with out using the Uni-syn again.
All this is so each carb sees the same air flow and if they are a matched pair of carbs, the fuel mixture will be the same. If they are not match 100%, the air flow can be the same but one mixture could be way off from the other.
Joe
