Let's distinguish between the pea-sized bubbles created by the bubbler valve/tube and the tiny bubbles generated at the electrodes.
Adjust the bubbler valve - that is what causes the pea-sized bubbles coming into the jar through the bubbler tube - and see the variation in this type of bubbling. The only reason for producing these bubbles is for creating water vapor. They are not for cooling the water off or adjusting the vacuum (more bubbles is not better, we need a very small amount of those).
Another way to distinguish this type of bubbles is to disconnect the negative electrode wire, start the engine and watch the bubbling. There would be no HHO bubbles since the electrolysis process is prevented.
To see the HHO bubbles without the air bubbles, disconnect the vacuum hose, or operate the electrolyzer SHORTLY (30 seconds) off of battery power when the engine is off. Now there will be no air bubbles, so the tiny bubbles that you see being produced at the electrodes are HHO. Re-connect the system normally after these tests.