Lead balls in carburetor

On the standard engine carby there are two small lead(?) balls which I think each sit in two traverse channels linked to either port.

When I reinstalled my carby a few months back I didn't put these balls in (very hard to do it seemed).

Car is running OK but the mixture seems a bit rich.
Could these missing balls be the reason?

What are they meant to do anyway?

Regards,
Russell