Stihl FS 550 Instruction Manual - Page 24

Fuel English / USA 4 3 3 3 2 1 Grass cutting blade 255-8 Brush knife 350-3 Brush knife 350-3 "Special" : Place the cutting tool (1) in position. Collar (see arrow) must engage the cutting tool's mounting hole. Cutting edges on grass cutting blade 255-8 and the circular saw blades must point clockwise. : Fit thrust washer (2) - convex side must face up. For mowing: : Fit rider plate (3) for mowing. 4 5 5 2 1 Circular saw blades 225 Circular saw blade 230 Circular saw blade 250 For sawing: : Fit rider plate (5) for sawing. : Block the output shaft. : Screw on nut (4) counterclockwise and tighten down firmly. Removing the cutting tool : Block the output shaft. : Unscrew the nut clockwise. If the mounting nut is too loose (cannot be tightened properly), fit a new one. 398BA050 KN This engine is certified to operate on unleaded gasoline and the STIHL twostroke engine oil at a mix ratio of 50:1. Your engine requires a mixture of highquality gasoline and quality two-stroke air cooled engine oil. Use mid-grade unleaded gasoline with a minimum octane rating of 89 (R+M/2). If the octane rating of the mid-grade gasoline in your area is lower, use premium unleaded fuel. Fuel with a lower octane rating may increase engine temperatures. This, in turn, increases the risk of piston seizure and damage to the engine. The chemical composition of the fuel is also important. Some fuel additives not only detrimentally affect elastomers (carburetor diaphragms, oil seals, fuel lines, etc.), but magnesium castings and catalytic converters as well. This could cause running problems or even damage the engine. For this reason STIHL recommends that you use only nationally recognized high-quality unleaded gasoline! FS 500, FS 550 23