Run ANY good oil - say anything that you'd find at a motorcycle shop, NOT Wally World! - at 40:1 and you'll never have an issue.
32:1 to 50:1 is generally the range that most will tell you to use w/modern day oils. In a water cooled machine I'd not worry about 50:1, but air cooled, I'd stay 32:1 to 40:1
I always found 40:1 easiest to do - 16oz (usually a bottle) to 5 gallons of fuel. Pretty straight forward.