good carbonation possible?

I know that a full sugar soda can get good carbonation and the proper bubbly fizzy that folks expect from soda, but I tried the low sugar/sugar free recipe in the Old Fashioned Soda Extracts brand extract. It consists of 1/8 tsp yeast for a 2lt bottle, and 2Tbs of sugar, with the rest of the sugar being Splenda or something for sweetening. The resulting soda seemed very flat. It didn't taste flat, but it was definitely missing something that the bubblies add.

Does anyone know of a good way to keep a home made soda relatively sugar free while still acting like a soda pop?

force carbonating is the simple way (investment required)

2 tbs sugar should have given you fizzies I'd think. With a "sugar free" recipe you *should* be able to let it sit at room temp indefinitely because once the yeasties eat the sugar, there's none left. How long did you let it sit before fridging?

Add a little more sugar next time, or let it sit longer.