Dont have he info for the 82 CR250 but the Honda manual for my 82 CR125 says it should be 20:1.
Having said that, two stroke oils have come a long way since 1982. I was using castor based (cause I love the smell) Shell M at 25:1 but it coked up the piston crown a bit so now im back using Castrol super TT at 33:1 without any issues.