Stihl HL 91 K Instruction Manual - Page 24

English Adjusting the Carburetor The carburetor of the machine has been adjusted at the factory for optimum performance and fuel efficiency in all operating states. Setting the idle speed Engine stops when idling N Turn the idle speed screw (LA) slowly clockwise until the engine runs smoothly. Cutting blades move when idling N Turn the idle speed adjusting screw (LA) slowly counterclockwise until the cutting blades stop moving WARNING If the cutting blades continue to move in idle even after adjustment, have the machine repaired by a STIHL servicing dealer. 0208BA036 KN Spark Plug If there is a loss of engine power, the machine is difficult to start or runs poorly at idle, first check the spark plug. Install a new spark plug after approximately 100 operating hours or earlier if the electrodes are eroded/corroded. The 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 degrade performance. Removing the spark plug 2 1 N Turn screw (1) in cap (2) until cap can be removed N Lay down cap 0208BA037 KN 3 N Pull off the spark plug boot (3) N Unscrew spark plug, Checking the Spark Plug A N Clean dirty spark plug. N Check electrode gap (A) and readjust if necessary - see chapter "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. 0208BA038 KN 000BA039 KN 22 HL 91 K