1L of gasoline contains about 8.8Kw of energy.
He's claiming to extract 2kw from .3L, 75% efficiency.
I'd be hesitant to say the generator alone can do that let alone the engine.
Neat idea but so far as I know can't even increase efficiency.
Because internal combustion engines work by difference of temperature, increasing intake temperature would increase exhaust temperature, meaning the same output power.
Adding water to the intake is sometimes used in turbo engines, it doesn't increase power it is used to cool intake air temp and exhaust temp to prevent damage to the turbo.
The bubler is basically a poor carb with a manual air valve. Using the original carb and a water injector would be far easier to experiment with.