BR 500, BR 550, BR 600
English
15
The STIHL 4-MIX engine features 
mixture lubrication and must be run on a 
fuel mixture of gasoline and engine oil.
It operates otherwise on the 4-stroke 
principle.
This engine is certified to operate on 
unleaded gasoline and the STIHL two-
stroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of high-
quality gasoline and two-stroke air 
cooled engine oil.
Use mid-grade unleaded gasoline with a 
minimum octane rating of 89 ((R+M)/2) 
and no more than 10% ethanol content.
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 
high-quality unleaded gasoline!
Gasoline with an ethanol content of 
more than 10% can cause running 
problems and major damage in engines 
and should not be used.
The ethanol content in gasoline affects 
engine running speed – it may be 
necessary to readjust the carburetor if 
you use fuels with various ethanol 
contents.
WARNING
To reduce the risk of personal injury 
from loss of control and/or contact with 
the running cutting tool, do not use your 
unit with incorrect idle adjustment. At 
correct idle speed, the cutting tool 
should not move.
If your power tool shows an incorrect idle 
adjustment, have your STIHL dealer 
check your power tool and make proper 
adjustments and repairs.
The idle speed and maximum speed of 
the engine change if you switch from a 
fuel with a certain ethanol content to 
another fuel with a much higher or lower 
ethanol content.
This problem can be avoided by always 
using fuel with the same ethanol 
content.
Use only STIHL two-stroke engine oil or 
equivalent high-quality two-stroke 
engine oils that are designed for use 
only in air cooled two-cycle engines.
We recommend STIHL HP Ultra 2-Cycle 
Engine Oil since it is specially 
formulated for use in STIHL engines.
Do not use BIA or TCW rated (two-
stroke water cooled) mix oils or other 
mix oils that state they are for use in both 
water cooled and air cooled engines 
(e.g., outboard motors, snowmobiles, 
chain saws, mopeds, etc.).
WARNING
Take care when handling gasoline. 
Avoid direct contact with the skin and 
avoid inhaling fuel vapor. When filling at 
the pump, first remove the container 
from your vehicle and place the 
container on the ground before filling. To 
reduce the risk of sparks from static 
discharge and resulting fire and/or 
explosion, do not fill fuel containers that 
are sitting in or on a vehicle or trailer.
4-MIX Engine Fuel