Last night I fired up the barbecue and got thinking about whether or not I could convert my 1974 GMC C1500 to Propane. Make it an Oil-Gas-Propane hybrid. Since Propane is cheap and not much less efficient than gas, so I know that I would save money on gas. (I ran the numbers a while back) I was thinking that I could start it up on gas and run it on propane. My issue is that I don't really want to install an electric fuel pump, I like the mechanical one, so what if I created a bypass valve that redirected the flow from the pump back into the tank? So I can switch it back to the carburetor at any time from a switch on my dash. I made a couple diagrams until I ran into a problem, I need to reference the flow of propane with the position of the throttle. Since propane is delivered as a gas, not a liquid, it won't fill the float bowl/get pushed by the accelerator pump, so I have to modify my carburetor. What do you think? I have most of the junk laying around to do this, I just need a way to reference the flow of propane with the throttle position. (I got some Ideas, but I would need some sort of low resistance gas valve in order the throttle to return, not an off the shelf one).