Hey guys... read about it here
Hydroxy Gas, they used to have a 400+ page document on how to make your own hydroxy gas generators. I can't find it right now since they changed their site around. I just saved it to my flashdrive.
A buddy at work constructed an "open bath" type generator, not the most efficient generator, but he got 5 more MPG on his Civic with no other mods. The trick is that you have to tap into the O2 sensor. You have to raise the voltage from the O2 sensor to the computer. It tells the computer that you're in a rich condition so it leans out the air/fuel mixture.
If you don't modify the O2 sensor then the O2 will see there's more Oxygen in the exhaust (from the generator breaking apart the hydrogen and oxygen) and richen up the engine getting you great power but half of your MPG.
FYI, disconnect everything when you take your vehicle for an inspection, otherwise they will red flag you as any modification to your emission equipment is illegal. With a carburetor it's easy... no electronics to tamper with.