Interesting point, heliduck. Here in Canada there are 2 main types of mogas - winter and summer. The winter type is more volatile than the summer type to aid starting in extremely cold weather like -40 or even colder in some places. I know from experience that using winter gas in a carbureted automobile in warm weather can cause vapour lock. So I wonder what would happen in a Robbie. I don't think I'd want to find out.
Further to my earlier post, 94 is the highest octane available - Sunoco 94. The lowest - regular - is 87.