Do I need BS34 mixture screw plug?

[Karkids]

I just took out the carbs to clean the idle circuit and I noticed the PO replaced the brass caps over the mix screws with tiny corks. I broke one of them. Are these essential like the rubber pilot tube plug or just a dust cover?
Thanks

 

[Jim]

I've never replaced the plugs after drilling them out. Not really any point to it.
My guess is whoever did it was thinking along the lines of a dust cover, but it doesn't really need one.