Here's the simplest electrical relation: THE HARDER THE PUSH (voltage), THE FASTER THE FLOW(amps). "Ohm's Law", can be written like this:

  VOLTS/OHMS = COULOMBS/SEC       The harder the push, the faster
                                  flows the charge

Note that coulombs per second is the same as "amperes." It says that a large voltage causes coulombs of charge to flow faster through a particular wire. But we usually think of current in terms of amps, not in terms of flowing charge. Here's the more common way to write Ohm's law:

  VOLTS/OHMS = AMPERES            Voltage across resistance causes current

Voltage divided by resistance equals current. Make the voltage twice as large, then the charges flow faster, and you get twice as much current. Make the voltage less, and the current becomes less.  Ohm's law has another feature: THE MORE FRICTION YOU HAVE, THE SLOWER THE FLOW

Therefor I have some suggestions: First check the wires you are using for the system, they might be offering a lot of resistance to the 12V input.

- Check to make sure the wiring is intact and electricity is flowing to the system from the battery. You can quickly and easily test this by using a 12 volt light bulb and making sure it lights.

- Check to see that the fuse is blown or not. You should be using a 5 amp fuse for every 1/4 teaspoon of baking soda to a quart of water

- Add more catalyst to increase water conductivity. (little by little)

If necessary, add more volts to the electrolyzer (this would be an extreme solution, not very recommendable)