I am so frustrated. I have taken these carbs apart so many times at this point and they are so clean. I start it up and drive a ways then as soon as it heats up I get sputtering and dying. I kill it then let it sit then it starts up again then same thing. I pull over and just let it idle and it eventually smooths out again. Is this just some bad gas that's going through? Could it be the fuel pump dying? It also starts backfiring when it stumbles. Any ideas?
Its so weird that it will run perfect for a few blocks if I let it cool off then it starts dying again.

Could be many things...
Bad Gas
clogged filter
clogged sock
bad pump
debris in tank

Usually bad gas means water in the tank. You could try some anti water agents like sea foam.

Before you get too carried away, what does the inside of the tank look like? Drain some fuel into a glass jar and look at it. If you have a mason jar, you can seal it and shake the fuel for 30 seconds. Excessive water will settle out at the bottom.

All new gas with ethanol is susceptible to water. Alcohol and water mix. If the water settles out, you can have it get into the carbs and cause bad running.

There is a sock filter on the supply line inside the tank. Check to see if it is clogged. Your tank is 40 years old now. It may need a refurbish.

I'm leaning toward bad gas, clogged filter or bad fuel pump. The clear inline filter I have has some debris in the bottom of it I can see. I think when I leave it a few minutes the fuel fills the lines than runs OK until I accelerate and it pulls harder than can be supplied. I also may look at accelerator pulps. Tomlinson says those can get dirty which would make sense BC when I accelerate I start to develop problem. Its just so weird BC it will be running rough then even out then go back to rough just idling

Start at the tank. Drain, clean and reseal if necessary. Replace the sock. Flush,clean or replace the fuel lines. Replace the filter. Start at the front and work your way back.

Is the gas tank venting properly?

Run a hose from carbs to a gas can. If it runs then its the tank, filter or your gas

Do the carbs pull hard enough to run without the pump if the tank is right next to them?

The nipples on my tank were packed with rust.

You need to run something through them to see if they are partly blocked.

I have a slightly different idea, try running a line from your fuel supply at the carbs to a gas can and turning the key to run (but not start).

If the fuel flow is steady and strong then it is not the tank, pump, lines, etc.

Get some pressure gauges and put them right before your carbs on both sides. Then see if you are getting 3 PSI steady. You can get those for $15 at a FLAPS.

Good luck.

John

Sounds like a fuel supply problem. Could even be vapor lock. Where's your pump located? It's better to push fuel than pull it. Did you change out all your lines? Do you have the SS tunnel lines? Do you have the thick phenolic (used to be phenolic anyhow) spacers under you manifolds? Did you replace the mesh tank sock?