After setting the float to the correct height as depicted, courtesy of Garry, & with the carburettor still upside down, you shouldn't be able to blow through a piece of fuel pipe connected to the banjo. Obvious, but worth stating
As the carburettor is turned to the correct orientation of normal positioning, then you should be able to blow air past the needle.
If you can do so, then so will fuel be able to enter. If it takes an almighty blast, then the needle &/or float may be sticking. Either that or the float needle has not been correctly assembled in the float tangs.