Stihl MM 55 STIHL YARD BOSS174 Product Instruction Manual - Page 21

Cutting attachment turns when idling N Turn the idle speed screw (LA) counterclockwise until the working tool stops running - then turn another 1/2 to 1 turn in the same direction If the working tool continues to keep moving in idle even after adjustment, have the machine checked by a servicing dealer. Erratic idling behavior, engine stalls despite correction of LA-setting, poor acceleration The idle setting is too lean - N Turn the low speed screw (L) counterclockwise (approx. 1/4 turn) until the engine runs and accelerates smoothly Erratic idling behavior The idle setting is too rich - N Turn the low speed screw (L) clockwise (approx. 1/4 turn) until the engine runs and accelerates smoothly Spark Plug If engine is down on power, difficult to start or runs poorly at idling speed, first check the spark plug. Fit a new spark plug after approx. 100 operating hours or earlier if the electrodes are badly eroded. Wrong fuel mix (too much engine oil in the gasoline), a dirty air filter and unfavorable running conditions (mostly at part throttle etc.) affect the condition of the spark plug. These factors cause deposits to form on the insulator nose which may result in trouble in operation. Remove the spark plug N Move the slide control to STOP-0 1 Checking the Spark Plug English 000BA039 KN A N Clean dirty spark plug. N Check electrode gap (A) and readjust if necessary - see "Specifications". N Use only resistor type spark plugs of the approved range. Rectify problems which have caused fouling of spark plug: - Too much oil in fuel mix. - Dirty air filter. - Unfavorable running conditions, e.g. operating at part load. 232BA081 KN N Unplug spark plug boot (1) N Unscrew spark plug MM 55, MM 55 C 19