My Cam with a lot of overlap, needs the Secondary Plates on my Holley 4150 opened more at idle so the Primary Plates are closed enough to allow idle mixture adjustment. It's a pain in the butt, The Carb must be removed, the adjustment is under the base, and it's trial and error until right.

Holley Marketing has a Solution!.... a tiny revised Bracket that allows easy adjustment while the engine is running. GREAT! Look it up.... $42 bucks? REALLY?

Did I buy it? Yup.... Does it work bitchin? Yup.... Am I butt-sore? Yup.... But it's kinda cool...