'83 RX-7 starts fine but won't keep running

[km4hr]

My factory original 1983 RX7 starts fine but cuts off after a few seconds. It acts like it's not getting enough gas. This started suddenly one day recently when I stopped at a stop sign.

If I pump the gas pedal slightly the engine will keep going. But if I hold the pedal steady at any position the engine shuts off. If I wait a few seconds it starts up fine and runs great for a few seconds. Then cuts off.

The car hadn't been driven in about 6 months so I thought the problem might be caused by bad gas. I drained the tank, purged the fuel line, and put in fresh gas. No luck, same problem. The car ran fine for a couple of miles before the problem started. The problem came on suddenly.

I also installed new plugs. It made little if any difference.

I'm not sure my problem is related to the fuel system. How does a rotary engine act when its skipping? I don't think this is an ignition problem but how can I be sure? I connected a timing light to each plug wire. It flashes on each wire indicating some kind of fire must be there. I'm not sure if that's a good test.

I rebuilt the carb about ten years ago. It's worked great ever since. Could something have suddenly plugged it?

The fuel pump seems to be working fine. It pumps a steady stream of gas when I disconnect the fuel line at the carb and drop it into a bucket. I don't know what the pressure is. It that critical?

What's the fuel return line for? I'm talking about the line that goes from the carb back to the tank. Does it carry fuel at all times or is it just for returning vapors to the tank?

Any help is greatly appreciated. I don't want to rebuild the carb only to find that's not the problem.