This has got to be the Nth time I advocate about the Nyberg Method, but here it goes:
In a typical 2-l bottle(I mainly use Welch's or some other bottles that are rectangular-shaped and slightly bigger in volume):
1. Add 1 cup of sugar. I sometimes try honey and it works just as well; CO2 production occurs sooner, actually.
2. Add 1teaspoon of baking soda, 2teaspoon of protein powder(or any natural powder rich in protein; I use soy powder which is cheaper)
3. Add 1 tablespoon of molasses. For better reference, you can search the exact recipe on-line or from recent issues of TAG.
4. Very tiny amount of yeast.
5. Add water; I use filtered water at room temperature. Try not to top as it might cause the bottle to burst should the pressure builds up. I'm telling you now because mine blew up and created loads of smelly mess

2-3 inches below the cap should be enough.
6. Sit patiently and wait. Things should start happening within 2-3 hours, if not a little sooner or later.
Mine usually lasts from 3-4 weeks, with the 2nd to 3rd weeks being the most steady and productive in terms of bubbling rate.
Paul