No fuel after start up

Several years ago, Mine worked perfect when cold but after the engine warmed up I could watch the filter empty then refill in cycles. The engine would go lean and stumble for a few seconds. I changed the sock, the rubber lines, and the fuel pump. No change. It took me a while to realize the filter wasn't really going empty. It was filling with fuel vapor flowing back from the carb bowl. One would think that the bowl vent would be sufficient. Even with the 73 model 2 brl. carb that has a much larger vent for vapor return system, same thing happened, just not as severe. Anyway... The fuel line for a 73 model has the fuel filter mounted vertically between alternator and timing cover. I think the fan keeps it cooler there. That and the thickest base gasket I could find put under the carb fixed it. A while later I found where to buy real gas. It doesn't perk so easy and doesn't perk away after shut down either.
So first thing to check, Is the bowl vent open? A little disc on the accelerator pump shaft lifted?
If you do change to the later model fuel line/filter configuration and buy the aftermarket reproduction line, you'll need to change to the later model fuel pump too. They moved the dang line connection point on it.