Looks like a combination tucker finger---twine disc---needle adjustment.

The twine discs are supposed to be adjusted depending on the billhook:  sisal hook or multi hook.  I've found they seem to work a little better adjusted toward the sisal hook setting.

The tucker fingers have a range where they work, then it's a no-go.  Set them close to the needle, even touching.  

Adjust the needles first.  They, too, have a range in which everything works, then it is a no-go.