Ok, mystery solved. I plumbed a bottle of gas directly to the fuel pump (1st photo) and started the car. No bubbles in the fuel pump, so it wasn't the pump or diaphragm. It was something upstream causing the bubbles. I then blew some compressed air up the fuel line to see if there were any blockages between the pump and the tank. I felt no resistance and heard air bubbles in the tank, so no blockages. But as soon as I released the air, gas came gushing out of the fuel line, which I quickly plugged back into the fuel pump. I went to the back of the car and took off the gas cap and sure enough I got a whoosh from pressure in the tank. The tank was not being vented properly! These cars do not use a vented gas cap but instead have a separate vent tube (2nd photo) that comes out right above the gas cap, which is hidden behind the spring loaded license plate bracket. The other end of the vent tube connects to the tank via a short length of rubber hose high on the driver's side of the tank. I pulled that hose off the tank and gave it a shot of air but nothing went through. Even at 100 psi I could not get air through the vent hose and tube. I then fished a length of rebar tie wire into both ends of the vent tube and eventually found the blockage about 4 inches in from where the vent pipe exits the car above the gas cap. It took quite a bit of prodding to break up the blockage and I blew the debris out with air applied to the tank end of the vent tube. I'm not sure what it was, but it looked like some hard mud from a small mud wasp or other small critter that was able to crawl up the vent tube. Jeez, what an ordeal, but at least its done. Now on to the next gremlin.
