[Rick Parker]

Holleys??
Replace the Cork (Holley OEM) or very small rubber "O" rings (Barry Grant/Demon) (interchangeable with each other too) that fit in the counter bored holes that the idle mixture screws thread into. These provide a seal to prevent air leaks and provide and elastic feature (like a nylock nut) to prevent the screws from moving. Or (Edelbrock/AFB type) use the very thin Locktite (green) that is intended to be applied after the screws are "set" It wicks into the threads. Easy to "Undo " as needed.
Any good speed shop or carburetor vendor should be able to supply them separately OR they are in a Carb rebuild kit too.