Something is amiss either with the float valve
With the O-ring sealing the float valve body into the carb.
How about leaving the float bowl off. Connecting to static fuel supply and moving the floats up and down manually. I know this is a pain due to the platic non-attached to anything float "tree" that is provided on these carbs.
Hopefully this way you can see where the problem lies.
Please remember to remove or turn off ALL ignition sources when doing this.
Don't want to burn down the shop.
Remember your FI bikes are new....I can only guess what those systems will look like in 2033. At that point, I'd guess you'd be wishing for simple ole carbs.
I've been lusting after a S10 for a while now....How do you like it?