Wow... he likes his baby food! But what bird wouldn't? It is so yummy.
As you probably already know, you have to taper it off gradually and monitor the bird's progress.
It is natural for birds to lose a *little* bit of weight when their diet is changed on them... especially when there is nothing else as yummy as formula. But i also know from experience that you cannot always tell whether or not your bird has acceptable levels of weight loss just by looking at them - especially if the bird is new to you. So to catch weight loss before it becomes an issue you should have a scale and weigh your bird regularly. Daily when weight is a known issue, as that will give you a better sense of the rate of weight loss, if any. Make sure you weigh at the same time each day, since weight varies a lot throughout the day. I weigh after the morning poop and before breakfast, since trial and error tells me that this is the time when weight varies the least from day to day. It is just part of the daily routine - poop, weight, medicine, breakfast!
You should have in mind a number below which your bird should not go, preferably one that is given to you by your vet. And weaning is a process. Don't taper down if your bird is anywhere close to this number.
As for tips to get your bird to eat more of these new foods, check out the following link for some of those:
http://www.avianstudios.com/wp-content/uploads/Foods-for-Different-Avian-Species3.pdf