Ron Novak's Do-It-Yourself Water Injection System
You can improve your car engine's starting ability, pickup, and fuel economy by constructing a homemade water injection system -- for a total cost of under five dollars! And you'll spend that small amount of money (heck, it takes more cash than that to buy one tank of gas nowadays!) entirely on parts -- because all the information you'll need to "inject" your own auto is right here in this article! ( Original article Mother earth 1979 )

Gilles,
Something I noticed in the diagram at your web page that might cause problems in the existing vacuum system.
If you cut the line as shown, and install the needle valve in series with other vacuum-operated devices, they may not perform properly because of the restriction. Perhaps it might be better to locate the valve on the branch of the tee?
Regards,
Ralph
Here is my rendition of the original 1979 Diagram with Ralph's recommendations.
GOSEE: Posting No: 7023 from our ALCOHOLFUEL FORUM.
