Best® 7S CR 1000 Engine Cleaner, proves starting and performance. Cleans dirty intake systems and spark plugs and frees sticky valves. Also removes gum, varnish and carbon deposits from engine exterior surfaces. Recommended for carburetors and fuel injectors. Works inside and outside the engine. Effective in both two-cycle and four-cycle engines, 7S CR 1000 eliminates engine ping and keeps carburetors and injector systems properly tuned. 7S CR 1000 is safe for fuel injectors, catalytic converters and emission control devices. It will not damage seals, gaskets, rubber or plastic materials commonly used in gasoline engines.