1976 flh....runs fine for about 10/15 minutes, then starts spitting, sputtering...like it is gas starved....checked for vapor lock....changed plugs...guess my next thought is the points

Is there an obstruction in your fuel line that feeds the carburetor from the tank itself?

I don't know if this will help you or not, but I've had several friends with Volkswagens & have run across this problem after they ran out of gas.
the fuel line ran close to the exhaust manifold & the gas would vaporize in the fuel line, causing a vapor lock in the line, starving the engine of fuel.
the fuel line had to be taken off at the carburetor & fuel sucked up through the line.
future problems were eliminated by rerouting the fuel line.

I don't think your problem is vapor lock. Your machine is just starving for fuel. Your problem can be solved by removing and cleaning your carburetor, changing the gaskets, changing filter , and checking for bad fuel lines. Your problem is very common. GOOD LUCK FRIEND.

sounds like a vapor lock. older cars needed a set of points . they kept firing times in sync with fuel delivery , valves opening/closing try that.

Check that the connection of the wires in the block connector (near the fuel tap) from the generator to the main loom is good. When checking the the ignition timing an ohm meter is connected to the black wire at this connector, sometimes causing the wire to 'pop' out of it's location and causing intermittent/complete ignition failure.

Its likely the fuel pump Ihave a 96 blazer and had to do mine last year they ware out and this one is no fun to do good luck

Hook a fuel preasure gauge to it and run it until it acts up then check the preasure, if the preasure goes low ,replace the fuelpump.

change the plug wires and check for a cracked coil

Sounds like plugged catalytic converter, Disconnect exhaust in front of Cat. and see what happens. Check to see if you are losing fluid from radiator.

mine did the same, I found out that the high speed jet was clogged, I pulled the fuel line off the filtor(going to the carb), stuck the line into a mixture of half gas half carb cleaner, I fanned it up and in 2 or 3 minutes it started running well, hope this helps.