AS400 on our network question.

We recently put our AS400 on a network. We get a sign on screen through telnet within the network but when we try and connect to the as400 from outside with it's external ip which gets nated, the packets seem to go to the 400 but don't return. Shouldn't the 400 still give a sign on screen to the outside ip request or is there as400 settings im missing. Assuming thefirewall is set up correctly.