Never heard of that! Unless you're talking about the fuel well plugs leaking.
Any mileage gains are acquired by adjusting how deep your metering rods are in your jets. THis is called the APT (adjustable part throttle). Accessible thru a plug on the front top of your carb.
Here's an awesome link for quads.
Quadrajet Info by Lars - Corvette Forum : DigitalCorvettes.com Corvette Forums