1955 Tbird stock 292, auto trans.  I usually adjust the idle to 500-600 RPM with the car in Drive.

I followed these instructions http://www.eatonbalancing.com/blog/2013/03/02/modifying-the-holley-teapot-four-barrel-carb-for-late-model-distributors/

"Once the carb is reinstalled on the engine, simply hook a hose at the new port on the carb and connect the other end of the hose to the vacuum advance chamber at the distributor.  With a timing light hooked up and with the engine running and idling, there should be no timing change with the hose either hooked or unhooked. 
When I connect the hose at idle, there is a vacuum signal at idle and the timing is increasing about 15 degrees.

I could NOT get the idle set to have no vacuum at idle from the new vacuum port on the carb.   The transition hole/slot (that provides vacuum to the distributor) is exposed as I raise the idle enough to keep the car running.   I removed the carb to double check everything.  Looking at the carb from the base, I could see the slightest increase to idle RPM starts exposing the transition slot, introducing vacuum to the distributor at idle, increasing timing 15 degrees additional.........about 25 BTDC

I tried adjusting the idle with a vacuum gauge in the carb's new vacuum port, at "0" vacuum the car would stall.  Has anyone ever drilled a hole in the butterfly to get the carb to idle and keep the transition slot at "0" vacuum or is there another solution?