This topic has been discussed extensively on this site. When I had 2 strokes, I ran 93 octane. The ratio really depends on how your bike is jetted. From the factory, you simply run what the manual recommends. For old bikes, you never know what the previous owner has done. I bought a RM 125 that the previous owner jetted as if it was a big bore. I installed a much smaller main jet and finally got it dialed in. The difference in size could be seen with the naked eye..thats bad. Many people dont know what they are doing when it comes to jetting. I ran 40:1 in my RM.