Persistent stalling after warm-up

[Carmine]

I can't believe so many people are just telling you to throw parts at this (not only in an era of junk aftermarket parts, but also introducing potential new problems). What is this? Facebook?

Backfiring through the carb is a sign you are lean, (fuel issue) backfiring through the muffler means raw fuel in the tailpipe (an ignition issue).

Keep a can of starting fluid with you (do they sell that in Florida?) Get it warmed up on a backroad. If it stalls, shoot some in the carb. If it fires, you have fuel shortage... Vapor lock.

if it doesn't fire, pull a sparkplug wire and use an extra spark plug, hold it on a ground and see if you are sparking across the gap. If no, see if you have spark from the coil by removing the wire at the distributor end and hold it 1/4" from a ground. No spark? Insert paper clip into the two female leads of the ballast wire (don't let the paper clip touch metal). Spark? Ballast resistor with a small break affected by heat. No spark? Could be the coil.

In other words, there are diagnostic process for all of these problems. None are complicated or cost more than $5 for the starting fluid.

My "guess", which is all anyone else is doing, is that you have a fuel-boil/vapor lock issue.

 

[Grannys67]

.... or the timing is way, way off now after having worked on it

sometimes I've just given the distributor a little twist on a non-running car and it will get it idling enough to put a light on it and fine tune it.

at this point i'd start looking at if your fuel pump isn't crapping out maybe

 

[Toolmanmike]

My 76 NYB 440, runs fine until it is really warmed up.
It developed this after a highway run.
Now, every time I drive her, she runs fine until well warmed up then the engine begins to stumble and miss finally stalling completely.
Once she stalls there is no restarting.
The starter just turns the motor over without any sign of ignition.
After about 20 minutes of waiting, I can re-start and usually get back home.
Occasionally when stepping on the gas she will back-fire through the carburetor.
I've checked and changed the fuel filter and replaced the ignition module.
Any ideas where I can look next?

You say "without any sign of ignition" Have you tested for spark when it won't start?

 

[Carmine]

Today I replaced the ballast resistor, coil and distributer pickup (gaped per manual) now it doesn't run at all on her own. If I squirt it with starter fluid, she'll fire then die. The wife is SO done with this car. Sad because we both loved cruising with the windows down.

Rude, but truthful translation:

“Today I threw parts at the car, based on a bunch of persistent wives tales and nonsense guesses that people insist upon making, since it's not their time/money. I found that adding fuel (starting fluid) has a cause/effect on the problem. I thus have a fueling problem. Since the car runs OK until warm, it's a fuel problem related to temperature. If fuel is vaporizing before it passes in liquid form through the carburetor, it will explode outside of the combustion chamber... aka "lean pop". Either the combination of more volatile ethanol fuel, or just a plain ol' physical problem (like a steel fuel line routed too close to a heat source) is taking my chariot outside the parameters for proper mechanical function. My spousal unit has expressed frustration because of a fear of being stranded. If people keep shooting expensive and time wasting guesses, I will be forced to give up something we enjoy [which always makes me sad to hear ].”