If I take a Corny to a party without bringing any CO2, the beer tends to get foamier and foamier as the pressure in the keg drops down. Eventually no liquid beer comes out.
So try a lower serving pressure with a longer pour, but not a really slow pour.
I think the beer might be overcarbed even for soda, but that would be a separate problem. I am not suggesting that the soda should carbed to the same level as beer if soda-like carbonation is what you desire.
Thanks as well, got some experimenting to do here. Yes, I am looking for a higher carb level similar to sods as that's what this lends itself to flavor and mouthfeel wise. At lower carb levels it tasted like flat root beer syrup:) The higher carb level makes it taste just like root beer with good fizz, just no head...........