Exactly. Many people here are using solutions that are such highly concentrated in sugar. The result is a wicked fast CO2 burst that last for a short while.
The best thing is to use a sugar concentration as DILUTE AS POSSIBLE. If you find that it's not going fast enough, more yeast is the best variable to fix to affect the rate of rxn...or for that fact increasing temperature is great too. By having the system dilute, the alcohol build up is much less, and the rate of rxn isn't explosive - meaning longer, consistent, and realistic CO2 output.
I use in two 2liter bottles each I use 1/2 cup of sugar, 1/4 teaspoon yeast, and fill with water 2 inches from the top. BTW, no baking soda since it kills yeast. Lasts me about 2.5 weeks at least and gives me 25+ ppm CO2 on my 20 gallon.