How many positions does your petcock have if any? If there is a RES this by passes the vacuum stop.
Still if there is fuel in the carb the bike will start and run for some time without fuel till it drains the bowl. I am sure you know this as I have read so many of your posts. This amount of time is WAY more than is needed to get the vacuum to the petcock and allow fuel to the bike.
I would replace all the hoses... the Chinese hoses are junk and will fail quickly. I have read this many times and have experienced it for myself.
Still check the auto choke. That is my best guess.