Q-jets are notorious for the well plugs leaking. Get the engine hot, remove the air cleaner, shut down the engine, hold the throttle full open and wait. After a little while you'll probably see a white vapor cloud coming from the carb. Leaking well plugs. Time for a rebuild.A lot of mechanics epoxy the existing well plugs but I never had any luck. They always leaked again. Here is where you can get o-ringed replacement plugs. Call them with your carb #. There is two sized plugs.
Carburetor Parts for Rochester Quadrajet, 4G, 2G & Carter AFB, AVS, Thermo-Quad Carburetors