My parts seller says that there is a difference between a 68 Riv with A/C vs. no A/C. What can this be?? Frank
Typically, the fuel-pump for an air-conditioned car has a second outlet, for a total of three fittings. One fitting is the intake from the fuel tank. The second is the outlet to the carburetor. The additional fitting is another outlet that is a fuel-return line going back to the fuel tank. When the A/C is running, the heat-load in the engine compartment is quite high due to the A/C condenser dumping it's heat in front of the radiator. This can cause vapor lock in the fuel lines. The return line from the fuel pump keeps a steady stream of gasoline circulating between the relatively cool fuel tank and the fuel pump. Thus, the fuel pump doesn't overheat, vaporize the gasoline within and stop pumping. The fuel pump can only pump liquid, not vapor. A bubble of gasoline vapor will just squeeze and not move the fuel. Eventually, your carb will run out of gas and the car will stall. It's like your brakes. If you get an air bubble inside the pedal gets 'spongy' - instead of moving fluid to the brake cylinders, it just squeezes the bubble when you press on the pedal.
Thanks. So if I get a pump for an A/C car, (which is all that is available; I have a non-A/C car) I can just cap the extra port? Frank
In short, yes - you can cap off the vapor return port. What size engine do you have in your Riviera? Because in '68, all the big-blocks (400 and 430) used a vapor-return system, even if not A/C equipped. In other words, you may need a pump with all three fittings anyway. In reading further, I find the only other difference between the vapor-return and non-vapor-return fuel pumps is this - the non-vapor pumps have tiny "leak-down" orifices in the check valves within the pump. The idea is that if the fuel lines overheat and the fuel vaporizes within during a 'hot soak' (ie - engine recently shut off), the excess pressure will back up through the check valves. Otherwise, the excess pressure might force the carb float valve off it's seat and flood the carburetor, making it harder to start. So, if you take a three-line fuel-pump and plug the vapor-return, you might have trouble re-starting the car on a hot-day after having shut it off for a few minutes.
Thanks for the response! I do have 2 hoses on the pump, so I have a return system. The pump I bought is way wrong anyway: it's arm is too short and it's ports are not right. O'Reilly's is closed today, but I'll switch it out tomorrow. Frank
Thanks for the response! I do have 2 hoses on the pump, so I have a return system. The pump I bought is way wrong anyway: it's arm is too short and it's ports are not right. O'Reilly's is closed today, but I'll switch it out tomorrow. I have the original 430. Frank
