Just a thought, but has anybody tried a heat insulating spacer twixt carb and engine? I rather suspect from reading the other entries here that heat creep might just be the last straw for an engine with other minor problems that alone or individually would have little or no noticable effect.
I once spent many happy hours boiling petrol over a bunsen burner and measuring how long it took the various components to boil off. A hot carburettor will also boil off the more volatile fractions so if there are some small air leaks, a weakening magneto, a slightly “iffy” plug, timing a bit off, well, you get the idea…
That was a potentially short sounding career – one mistake and you’re fired! Seriously though this sort of testing is done all the time by the producers on fuels of all types. In truth quality control is very tight indeed so don’t blame the petrol.
After experiencing the problem of non-starting when hot and also cutting out completely when riding, it was suggested to me that I remove the contact breaker assembly, clean off the interior making sure that the brush is clean and re-assemble. I find that this exercise helps to solve the problem.