oil blockoffs

I just bought a 95 speedster (657x times 2) that has the oil blockoffs installed, I still have the oil (XP-S 2 Stroke Synthetic) going to the crankcase via the oil resivor, What I need to know is (1)whats the best ratio to use, 40:1 or 50:1 ? (2) what can I use for a premix? thats going to be...