[jhv48]

You can adjust and readjust the vacuum secondary carb over and over but if you want that immediate power, you’ll have to ditch the carb and put on a double pumper.
Just buy/borrow one and stick it on. You won’t regret it. Even on Holley’s web site they recommend mechanical secondary carbs instead of vacuum secondary carbs for our cars due to their light weight.
I’ve done it twice on two different cobras. Both came with vacuum secondary carbs. One a Holley street avenger the other an Edelbrock AVS. Fiddled with both until I decided to bite the bullet and buy a double pumper. Woke those engines right up and now I can break the tires loose in fourth gear if I’m not careful. And that’s with sticky 180 treadwear 315’s.
Just do it.