I agree the factory carb is lacking. A twin Mikuni would be the ultimate setup, but there is no room for them. I've seen single Mikuni carb adapted on, but I'm not sold on the idea of a single carb on a 2 cylinder, lack of tuning. I will stay with a 2 barrel.
I am working on tuning a stock big block carb(35hp) to run on a 23hp. The venturi is much bigger. Initial testing is looking very good, especially for the price(yet to be announced).