Keep treating and praising whenever he does walk, be fair and don't push him too hard. Patience!! My pup hesitated to walk, as well. He is still very young and getting used to everything, he knows what he has on and this is probably confusing him. Have you tried keeping the leash on inside and walking him around with it?
Keep it short and sweet don't go too far, I will bet you in one or two weeks, he will be walking much nicer. In one month you will see how much further he can walk than you can