Possibly . . . but it will be easy to see if that is where the leak is, so check it well before digging into the carbs. There are also a myriad of small hoses from there that feed all the carbs, so a thorough inspection of what you can see, with the air filter housing removed, is also in order.Since the fuel leaks only when motorcycle is working and it turns on without problems I think shut off valve shouldn't be a problem, right?
Good luck tomorrow.