Most foaming is caused by contamination. You have to be very careful when you assemble your unit that your plates are perfectly clean.
Try draining you system and flushing it with distilled water. Refill your reservoir with clean distilled water and apply 12 volt power. There should be enough residual KOH for you to get some amp draw. Run for awhile then repeat process until you can no longer draw any amperage. Then refill with normal KOH solution (make, of course, with distilled water).
Also, excessive amperage will make foaming worse, but it usually isn't the root of the foaming problem.
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.