Assuming the bike ran good in the past then started acting funny after sitting, first thing I would do is pull the carbs and entirely clean them.

Once you got the carbs clean, especially if you found some crud in there , I'd drain any old fuel from the tank. Next I would probably pull the fuel tap and make sure tank is clean. Hopefully the fuel tap screen is doing its thing, but I never trust those so you might add an inline paper filter. Last thing you want to do is fill your clean carbs up with crud!

Let us know how it goes.