The Carbon Guard additive is a gasoline additive formulated to minimize carbon deposit build-up in 2-Stroke and 4-Stroke marine engines. Add Carbon Guard to the fuel tank each time you add gasoline. For 2-Stroke and DI Engines - add 1 oz. of Carbon Guard for every 8 gallons of gasoline. For 4-Stroke Engines - add 1 oz. of Carbon Guard for every 16 gallons of gasoline. It is recommended that oil be changed on 4-Stroke engines after on application of Carbon Guard. 2-Stroke engines with an excess of 100 hours of operation and not previously treated with Carbon Guard should be treated with engine tuner before beginning use of Carbon Guard.