I see no other practical way of determining the relationship of the throttle butterfly to the transfer slot than a visual inspection of the carb viewed from the bottom. Merely backing down the idle speed by way of the linkage adjustment is not reliable. Backing down idle speed from 1000 to 750 by this method does not insure that the transition slot is now covered and that the manifold vacuum is now present to only the idle circuit. Only a visual inspection can establish this fact accurately.
