The venturi doesn't effect the idle gap, as it doesn't travel all the way down to the slide, but the smaller venturis do make it harder to see the idle gap if your setting it manually.
Even if you set the gap manually with a piece of wire etc, still use the 7 sec pinch method to finally set the idle gap. This is the ultimate way to ensure the gap is correct for your particular motor and set up. This is a dynamic method with the motor actually running, as opposed to a static method where you are really only guessing the gap is correct.