Most of the problems associated with missfires / rough running from bikes that have stood for a comparativelly short time are from the petrol contaminating the small cross-drillings within the carb body.
The various additives settle out & forms a laquer that can not be cleaned out by air blasting / pipe cleaners etc.
On any old bike that has stood for a while, rather than spend loads of money & time on the above probelms, strip the carbs to basics & get them ultra-sonic cleaned.
It made a massive difference to my old gixer.