32
English / USA
FS 500, FS 550
Change the air intake to the winter mode 
to help prevent air filter and carburetor 
icing at temperatures below 50°F 
(+10°C).
: Pull out the plug, turn it around and 
refit it so that the openings face the 
clutch housing.
Change the air intake back to the 
summer mode when the outside 
temperature is above 70°F (+20°C):
: Pull out the plug, turn it around and 
refit it so that the openings face 
outward. 
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 "Starting / 
Stopping the Engine".
: Clean dirty spark plug.
: Check electrode gap (A) and 
readjust if necessary – see 
"Specifications".
: 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.
Fit a new spark plug after approx. 
100 operating hours 
or earlier if the electrodes are badly 
eroded.
Winter Operation
398BA021 KN
Checking the Spark Plug
000BA002 KN