I would look to make the motor leaner first by leaning the idle mixture screws down on all three carbs., then go from there thumbs
My old pump gas six pack liked #63 jets in the center carb and 1/4 to 1/3 turn out from gently bottomed out on the idle mixture screws on the outboard carbs and 3/4 to 1 full turn out on the center carb. scope
What carb. List # are you working on? If they are replacement carbs. (-1 or -2) your probably dealing with a really lean set up from Holley for smog. Have you enlarged the outboard carb. main fuel feeds in the plates? My carbs ran the fastest ET and MPH with 13.3 AFR at WOT above 5500 RPM shruggy
It FELT better at 11.8 to 12.5 AFR shruggy work

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)