I think you will find that the only adjustment is the idle stop screw. It has no impact on a barrel/needle carb except to limit how far the barrel/needle drops down and thus the idle speed. Pick a point where the barrel isn’t all the way closed and then adjust to get the best idle speed.
The China-made OMC 2hp is a pretty chintzy bit of work when compared to the old Junior/Colt that it replaced. However, they do run pretty well if everything is there and in good shape. The plastic parts of the cowl are utter crap though….