Does it restart immediatley when after it quits, or do you have to wait a bit. Have you tried pulling the choke when it does this..?? I have had a speck of something in the main jet on my Super C, and a quick tug on the choke will take it on through.
If it takes a bit, I'd have tools along to pull a plug, turn the engine over, and check for spark. If you have spark, maybe pull the plug in the bottom of the carb, and see if fuel is being delivered.
There is a screen in the elbow going into the carb, but if it's plugged, doubt it would run that long.
I'm assuming that is an electrical fuel pump. I have had smaller units quit pumping fuel when the engine has warmed up to op. temps.
Then again, years ago, Dad had a Farmall A that had similar symptoms. A wasp abdomen in the fuel tank was the culprit. A perfect fit to seal off the standpipe.
If it does it pretty regular at the 20-30 minute mark, I'd also suspect the coil.