there is a clamp that holds the carb to the manifold boot you can loosen it up and work the carb out of the boot then tilt up enough to get to that screw.
it also helps to take the choke cable and lever out of its bracket 17mm wrench and then just lift it out, when you put it back snug the nut till it holds friction on the lever.
It is the D screw in the recess on the left side of the pic
