When I disconnected the tubing I thought it was just an air pressure type connection but apparently the system required fluid that was less compressable to sense weight on the seat. In retrospect I can understand why it was designed that way but it sure was not expected.
As an engineer I can appreciate the design involved with modern vehicle systems but I am very much an old school car person so as much as I understand the potential of modern systems (like electronic fuel injection) I choose to use an old fashion carburetor.
