I got a good look at one of these today. Impco regulator with a electric lock off. The fuel hose goes to the top of the carb. There is a "T" in the fuel hose with a small diameter (vacuum line) hose that goes to the base of the carb, like where a vacuum hose would hook up. In the "T" is a valve that you can adjust how much flow the small hose has. This is the idle mixture control, like the pilot circuit on a gas carb. Just under the base of the carb is the 1/2" water hose that goes to the Impco with a thermostat in it. On the very top of the carb is the gasoline inlet. I would think on a duel fuel system you have another electric lock off on the gasoline line somewhere by the carb