I found it easier mixing 4 1/2 litres at a time, pouring in 150cc of oil (4500cc / 30:1 = 150cc)
As most mixing jugs are either 5 or 6 litres it made it easy.
Try and buy yourself a measuring tube/cup with small increments for the oil as the marking on most jugs are not accurate enough.
Don't forget to invest in a "weather station" as well for the jetting.

What year is the RS?