Stihl BR 400 Instruction Manual - Page 19

000BA039 KN 000BA036 TR A 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. If engine is down on power, difficult to start or runs poorly at idling speed, first check the spark plug. • Remove spark plug see chapter "Starting": Clean dirty spark plug. •• Check electrode gap it should be 0.5mm/0.02" - • readjust if necessary. Use only resistor type spark plugs of the approved range. Rectify problems which have caused fouling of spark plug: Incorrect carburetor setting, too much oil in fuel mix, dirty air filter, unfavorable running conditions, e.g. operating at part load. 1 • Fit a new spark plug after approx. 100 operating hours or earlier if the electrodes are badly eroded. To reduce the risk of fire and burn injury, use only spark plugs authorized by STIHL (see "Specifications"). Always press spark plug boot snugly onto spark plug terminal of the proper size. (Note: If terminal has detachable SAE adapter nut, it must be attached.) A loose connection between spark plug terminal and ignition wire connector in the boot may create arcing that could ignite combustible fumes and cause a fire.