The FASD is, in our minds, nothing more than a small third carburetor which shuts itself off when the coolant temperature gets warm enough. First, compliments of Kelvin Dodd at Moss Motors we have the Zenith Stromberg Repair Manual with the FASD section, as well as the water chokes. Second, we have the two patents granted to the Zenith Carburetor Company, US Patent 3,967,610 and its companion (a Continuation-In-Part, US Patent 4,069,802) which cements the company's claims on the operation a little better. In addition, for your reading pleasure, we've extracted two articles from TWOA Newsletters 19 and 20 covering theory, operation and disassembly as well. We hope this demystifies this enigmatic little device.
The British Leyland Factory Service Manual for the Zenith Stromberg series of Carburetors.
The FASD information begins on page 15 of the PDF file.