Those two screws are low and high speed mixture adjustments. You can see on the lever attached to the throttle butterfly (just above the mixture screws) the tang which would normally rest against the idle speed screw, but there is no idle speed screw, and no boss on the carburetor body to screw it through. Instead there is a big block holding the throttle pin: the position of that block sets the idle speed. I don't know how they get acceptable idle speed control that way, but it seems they do.