JohnsonEvinrude Carbon Guard Fuel Additive 12oz JohnsonEvinrude Carbon Guard is a gasoline additive formulated to minimize deposit build-up in 2-cycle and 4-cycle marine engines when used as directed. Carbon Guard Benefits Reduced possibility of piston ring sticking Reduced carbon build up on 4-cycle valves Better overall engine performance Increased engine life For 2-Cycle and DI engines Add 1 oz. of Carbon Guard for every 8 gallons of gasoline. For 4-Cycle engines Add 1 oz. of Carbon Guard for