Holley Jet size

Mattax said

4. Turn the carb upside down and turn the throttle screw until the throttle is closed. Turn it in until it just touches and count how many turns until 0.020" of the transition slots show. Write that number down. Count how many turns of the screw is needed to get .030 and .040 visible. Write those numbers down.
Now you're ready to go try the carb out.

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I am not sure if this is referring to the primary or secondary side, but the secondary side will have a stop screw that sets the 'at rest' secondary throttle opening. You will want to set that stop screw so that the secondary transition slots are showing about as much height as width when the secondaries are fully closed. (I.e.: Slot exposure is 'square'.)

This will get adjusted when you get to the point of testing light off-idle accelerations cruising around at low speeds. It also effects idle vacuum and interacts with the PCV valve idle airflow. Both will effect idle air quantity and that effects not only idle, but also how the transition phase operates.