Let him eat. My guys pig out in the fall before they go off food in the winter. I have a 1600 gram black pastel that locks like a champ.
He might just not like the new girls. Ball pythons hate change, and my established pairs always lock first. Sometimes it takes them a few months to get used to a new mate.
And sometimes they just don't like a particular girl, or vice versa. Have some back-up males lined up, in case he's still not locking with her in the spring.