Your engine calls for a 50:1 gas to oil ratio. If you are using a common 6 gallon tank, put a pint of TC-W3 rated outboard oil in there and you will have a 48:1 mix. That is what is most of us do because it is so easy and doesn't leave us with partially full containers.
If you are trying to mix a smaller amount of fuel, you can pick up a measuring bottle at most marine outlet stores that is marked in different ratios and for different gallons and ounces.
Or just use math to figure what you need 16 oz to 6 gals, 8 oz to 3 gals, 4 oz to 1.5 gals, etc. are all 50:1
