Racing brew for old bike
My old shortstroke Manx Norton use to run quite nicely on 50/50 super unleaded/avgas and a splash of proboost octane enhancer. Any avgas always made plugs difficult to read to get the jetting right though. I was told not to use 100% avgas as it is designed for quite slow revving engines and would struggle to get complete combustion in my old 7000 rpm motor.