Stihl MS 391

Reduced-Emission Engine Technology - Caring for Nature
The STIHL Inc. “Caring for Nature” seal identifies its powered products that are more environmentally conscious, producing zero or low exhaust emissions. STIHL Inc. defines “low exhaust emissions” as being cleaner than EPA and/or CARB exhaust emission standards.

Pre-Separation Air Filtration System
This time-saving technology boosts the efficiency of the engine’s filter system, doubling the time between air filter cleanings. Air drawn into the engine is first separated via centrifugal force, ejecting the heavier dirt particles before being routed to the air filter. This pre-separation means less dirt to be captured by the air filter, resulting in less frequent cleaning and maintenance.

Anti-Vibration System
STIHL has developed a system for minimizing the vibration levels of handheld outdoor power equipment. The STIHL anti-vibration system helps reduce operator fatigue and provides a more comfortable working experience.

IntelliCarb™ Compensating Carburetor
The IntelliCarb™ Compensating Carburetor is designed to automatically adjust the air/fuel ratio when the air filter becomes restricted or partially clogged and maintains the engine’s correct RPM. IntelliCarb™ uses air from the clean side of the air filter to control the diaphragm and flow of fuel. As the air filter becomes dirty and less air is available for the carburetor, the IntelliCarb™ system adjusts the fuel flow to compensate for the decrease in air flow. This is in contrast to typical carburetors that utilize this air from the “dirty” side of the air box.

Side-Access Chain Tensioner
The side-access chain tensioner makes it much more convenient for the user to adjust the saw chain with a bar wrench as opposed to the typical location of the guide bar adjustment screw.

Note: STIHL recommends #3624 (33 RS3 72) OILOMATIC® saw chain and 20" 3003 008 8921 Ematic™ guide bar combination. Compatible guide bar ranges: 16" to 20"