Honda 2417 Gcv 530 Engine Surging

[Kurn]

I'm having the same problem with mine in a Toro zero turn. Tried just about everything-it does smooth out with a little choke and/or the deck engaged. Seems to be too lean to me. If I were to drill out the main jets, what would I drill them to? Or are bigger jets or a different carb available? Otherwise, it runs great.