Mercury - Carburetor Primer Plunger 8HP-9.9HP FourStroke Outboards Precision Fit 853830001. Overview. If you've spent enough time on the water, you know that the little things can make all the difference. The Mercury Quicksilver 853830001 Carburetor Primer Plunger is one of those small but essential parts that make every start-up feel effortless. Designed for Mercury 8HP and 9.9HP FourStroke carbureted outboards, this plunger ensures your engine gets the perfect burst of fuel to fire up smoothly