How many bubbles per second enter your Electrolyzer via the bubbler tube when the engine is at idle? (gasoline engines). Too much air coming in means too much water vapor production and fast water consumption.
Adjust the bubbler valve so that with the jar hooked up to the vacuum and the car at idle, you have AT MOST 1 to 3 bubbles per second coming into the water through the bubbler tube. You don't need much water vapor at all.
Having the bubbler valve completely closed - no air coming into the jar - is an option for the electrolyzer.
For the vaporizer, you need some air coming in, so 1 to 3 bubbles per second may be the ideal adjustment. And you only need one cell - more jars will not increase gas mileage.
For a multi cell HHO system, you want 1 to 3 bubbles per second for the entire system - that would be 1 bubble every 2 to 6 seconds for each jar in a 6-cell system.