I am probably risking my life jumping in at this point, but if it were me I would beg, borrow, or steal a carb off of a working engine and put it on and see what happens. It is not a tough job on this engine.
You did not list a rebuild of the carb - and carbs can actually wear out. In addition, a proper rebuild requires compressed air to really clean out the jets.
If this failied I would then get a compression guage - acheapy from Pet Boys - and do a real test.