Stihl MS 171 Product Instruction Manual - Page 43
Engine Management, Adjusting the Carburetor
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Engine Management Adjusting the Carburetor Adjusting idle speed English Exhaust emissions are controlled by the design of the fundamental engine parameters and components (e.g. carburation, ignition, timing and valve or port timing) without the addition of any major hardware. General information The carburetor comes from the factory with a standard setting. This setting provides an optimum fuel-air mixture under most operating conditions. With this carburetor it is only possible to correct the adjusting screws within fine limits. Standard setting N Switch off the engine. N Check the air filter and clean or replace if necessary. N Check the spark arresting screen (country-specific) in the muffler and clean or replace if necessary. HL 3/4 1 LA N Turn high speed screw (H) counterclockwise as far as stop (no more than 3/4 turn). N Turn the low speed screw (L) carefully clockwise as far as stop, then turn it back 1 turn. 533BA010 KN Engine stops while idling N Turn the low speed screw (L) carefully clockwise as far as stop, then turn it back 1 turn. N Turn the idle speed screw (LA) clockwise until the chain begins to run - then back it off 2 turns. Chain runs when engine is idling N Turn the low speed screw (L) carefully clockwise as far as stop, then turn it back 1 turn. N Turn the idle speed screw (LA) counterclockwise until the chain begins to run - then turn it another 2 turns in the same direction. If the chain continues moving when the engine is idling, have your saw checked and repaired by your servicing dealer. Erratic idling behavior, poor acceleration (even though standard setting of low speed screw is correct) Idle setting is too lean - N Idle setting is too lean: Turn the low speed screw (L) counterclockwise until the engine runs and accelerates smoothly. It is usually necessary to change the setting of the idle speed screw (LA) after every correction to the low speed screw (L). Fine tuning for operation at high altitude MS 171, MS 181, MS 181 C, MS 211, MS 211 C 41