Doby, I think you have it right. The later 97 seems somewhat of a compromise. They have the same vacuum source just above the closed throttle plate as a 8BA 94 but at least the one I have, is not connected to a venturi source. The base does have a extra hole for connection to the center bowl so maybe a special bowl with the proper venturi source has been changed out on the example I have. It probably performs better than a standard 97, but not as good as a 8BA 94.