Moped Army

Well I just started up my revival after having it stored for the past few months. I drained all the fuel out of the tank and carb. Put new fuel in today and she started up fine. After riding for a while she would die, then eventually restart. This kept happening more and more often and then it got really hard to start back up. I noticed there was air in about half of the fuel line towards the carb. My fuel line curves around a little bit but it has worked all last season just fine. Is there supposed to be any air in there? If not, why does air keep getting in there and killing my engine?