There's a handy chart on page two of this PDF, discussing vapor to liquid ratios of various fuel types.
https://www.grabner-instruments.com/...5-e640bdc7e338
It's important to note that we are talking about temperatures specific to the liquid fuel in use. At around 150 degrees the temperature common e10 pump gas will be about 80% vapor. What's occurring at this point is that your fuel pump is compressing the vapor and is no longer able to supply liquid fuel to the carb bowl. As engine speed slows and fuel consumption falls, the force of the vapor will stop liquid fuel from entering the venturis and the engine will stall.
The chart in that PDF also doesn't take into account fuel system pressure. If you read through the full work you might ask yourself how anything, even modern vehicles avoid vapor lock. A big reason is the fact that the systems of modern vehicles are under a good bit of pressure. 43psi for most early EFI automobiles while direct injected vehicles see fuel pressures at the nozzles of up to 1500psi. Just like your cooling system, the fuel under pressure will resist boiling.
If your engine runs at 200 degrees and your fuel flow through the system is slow enough due to low engine speeds, eventually with an e10 mixture, you're going to start seeing issues with vapor lock as components soak up all that heat and transfer it to the liquid fuel. Using a heat insulator between the carb and the fuel pump which are in direct contact with the engine block slows the heat build up in those components, but they will eventually soak from the ambient under hood temperatures.
Using gasoline that has no ethanol blending is your best choice. It is unfortunately becoming harder and harder to find at local pumps however. You can of course buy your own fuel and pump it at home, but then you limit your travel distance. This is why I'm an advocate for modernization of these components to deal with standard pump fuel.