A full carb rebuild probably isn't needed, just clean out the offending float needle seat. You can do that by just dropping the float bowl, carbs still in place. Probably a good idea to have a look in the float bowls since the bike is new to you. That will tell you how far you need to go on the carbs. If the bowls are all dirty and gummed up inside then yes, you may need to go through them further.