Quick Fuel Secondary air adjustment

[AC Ventura]

Hi guys from London, UK. I hope you are all okay, although it seems we are all in the same boat. Not so good here. Most businesses closed, most people off work and we are all pretty much forced to stay at home and strictly no socialising. All Motor and other sport including Formula One, Wimbledon etc have been cancelled. Plus our Prime Minister in intensive care. The most challenging times in my lifetime that’s for sure.
So, I have some time to try and get my new QFT fuelled 427FE running right. Set the corner idles with a vac gauge, and now getting 9.5” at about 850-900 idle, where it was 8”. I’m running a fairly big cam and the plugs are still black, after idling. I’ve read about drilling holes in the butterfly’s to introduce some air, but then found this note in the instructions.

NOTE: Secondary idle air can be adjusted externally. While this is a convenient tuning aid in cases where the primary throttle plates must be opened considerably to compensate for a radical camshaft profile, it should not be opened more the 1 1⁄2 turns from base as it could cause a hesitation at wide-open throttle. Consult a carburetor tuning book to ensure proper primary throttle plate alignment.

Does anybody know what form this externally idle adjustment is and where is it located? Surely, they don’t just mean open the throttle to higher idle?