I think you just have to take the carburettors apart and clean then really good. Blow all the orifices with compressed air. Normally you dont have to replace anything. Probably it's some oxide in the float bowl that comes from some water in the petrol. If you are careful you don't have to by new gaskets either. Check the rubber-things between the carb and the cylinder head for leaks! see: http://www.xs11.com/faq/faqboots.shtml
Some parts as Float Bowl Gasket, and Float Needle and Seat are awailable. See for example; https://www.partsnmoreonline.com/PNMSite/XV%20Virago%2048-1412%20Carb%20rebuild%20kit.htm
Good luck!