without seeing the condition of the different parts of carb oner cant say for sure where is the problem,,
the best thing that u can do in this case is get replaced the defective parts of ur carb with those of ok parts f,,u can ask mechanic to arrange them for u or get them from a fellows bike if u have, once it is determined that the issue is resolved then u may purchase it,,
also there could be leak in joints somewher between carb or the entire path,,from filter t carb to engine
however as a matter of fact a carb provides fuel o ur engine throughout the rpm range,,where is exactly the issue at slow speeds?
medium speeeds?
high speeds..
each of the above ranges are controlled by different circuits of carb,, once the problem is identified u can take corrective action,,