Late BS38 carbs will make your XS run as good as almost any carburetor, if they are clean, have proper brass for the year, and are adjusted correctly.
For replacements; Mikuni VM34's are popular, mostly because they aren't expensive for a brand name carburetor. There's lots of jetting info available for them. What year are your BS38s? Pictures especially from the intake bell side would help us ID them if there's a question.
Have you read and applied the carb guide info?
Found in tech:
http://www.amckayltd.com/carbguide.pdf
Do you have the correct brass in them for the year? Many, most "carb kits" have the wrong or inferior brass parts in them.
View attachment 246968