23FS 500, FS 550
English / USA
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.
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.
This engine is certified to operate on 
unleaded gasoline and the STIHL two-
stroke engine oil at a mix ratio of 50:1.
Your two-stroke engine requires a 
mixture of high-quality 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!
1
3
3
2
1
3
4
4
5
5
2
398BA050 KN
Fuel