Stihl KM 91 R Product Instruction Manual - Page 19

Spark Plug Checking the Spark Plug English If the engine is down on power, difficult to start or runs poorly at idling speed, first check the spark plug. Install a new spark plug after approx. 100 operating hours or earlier if the electrodes are badly 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 1 2 3 N Remove the cover (1). N Pull off the spark plug boot (2). N Unscrew the spark plug (3). 0000-GXX 0537-A0 000BA039 KN 0000-GXX-1831-A0 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. 1 3 2 WARNING To reduce the risk of fire and burn injury, use only spark plugs authorized by STIHL. Always press the spark plug boot (1) snugly onto the spark plug terminal (2). Do not use a spark plug with a detachable SAE adapter terminal (3). Arcing may occur that could ignite combustible fumes and cause a fire. This can result in serious injuries or damage to property. N Only use resistor type spark plugs with solid, non-threaded terminals Installing the Spark Plug N Screw the spark plug (3) into the cylinder. N Tighten down the spark plug (3) with the combination wrench. KM 91 R 17