Carburetor Cover & Special Screw

I was curious how important the "Cover" (#13) is that is screwed into the carb body over the main and pilot air jets. I have a rack of carbs and only one of the carbs has a threaded slot for the "special screw" (#14) that holds the cover on.

I'm assuming that the cover helps to provide non-turbulent air and therefore better airflow into the air jets. However, three of my carbs have the hole drilled out for the cover "special screw", but they aren't threaded.

My 1980 650 had the covers over the air jets.

Thanks,
Blake

 

http://www.xjbikes.com/forums/threa...tion-if-these-parts-have-been-removed.119132/
forget about them, you don't need them. that's why their not tapped
early models had them, later ones didn't

 

Thanks