Quote:
Originally Posted by toolboxchev
The larger center port is for the PCV valve on the Valve Cover. There is a port on the back side of the carb for Manifold vacuum if needed.
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Partly correct.
Large port front and back are manifold vacuum. Usually front is for pcv. Back one for power brakes. Front one can be tee’d like in the pic for the pcv and canister use. Factory did that mid 80’s.