With AED adjustable jet plates you can tune your vacuum secondary carburetor without buying multiple jet plates. Just remove the bowl and change jets like a conventional metering block. The advantage is that you can use all of your existing components like fuel lines and bowl screws and not increase the length of your carburetor. Great for multiple carb applications where carb length is a problem, these AED adjustable jet plates are machined from 6061 billet and are anodized for appearance and longevity.