At four months he is a little young he most likely doesn't see what your offering him as food. I would try this; first thing in the morning when he will be most hungry (after the morning poop) place him on a small table top perch and sit down to your morning breakfast (fresh fruit, scrambled eggs, a little granola ect.) I know it sounds healthy, well too bad, join the rest of us who eat better since we have birds, cause our babies need to learn to eat good things and learning by watching us, and you offering some of your breakfast to them from your plate. Remember to create some drama over everything you offer to them. I hope this gives you some ideas on how to get your fid to try new foods. Keep us updated on your progress.