A dual carb intake creates less vacuum under load at each carb than a single carb intake but hooking directly to the intake manifold will subject the vacuum advance to approximately 22lbs of vacuum at idle instead of 0lbs if hooked to the carb. Hooked to the carb vacuum increases under load from 0lbs and then decreases as it reaches WOT. Hooked to the intake manifold 22lbs decreases under load as it reaches WOT. This basically defeats the gas mileage benefits of a vacuum advance.
I would recommend putting a T in the line and going to both carbs.
