I have a 1980 Moto Morini that will only run well on higher octane fuel. For example the Shell V power type of fuel. I tried Avgas 100LL from the flying club. It was a good price as it was the ex daily test samples. I have used it straight and it runs brilliantly but also found that runing it with 1/4 to 1/3 100LL worked well.
I now have a lead substitute slug in the tank I think it is tin, not sure if it works or not but still no burnt out valves many years later.