RC,
I tried Potassium Carbonate a couple of time, and could never get it to product much. To bad, because it a lot less caustic than KOH. If you follow koya1893's advice, you should have a good system. I just wanted to jump in to let you know my first hand experience with Potassium Carbonate.
Steve
1991 Plymouth Acclaim 3L V6.
1 dry cells with nineteen 6"x8" 316L ss plates, driven by constant current PWM set at 35 amps (13.3V at PWM). 28% KOH electrolyte. Total measured output 2.5 lpm. Mileage went from 18 to 26 mpg, all city driving (44% increase). EFIE set at .370 and I still need to play with ignition timing.