Stihl 038 - Notes on Operation; Starting for first time; During operation; Spark plug

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Notes on Operation
Starting for first time
A factory new machine should not be run at high revs (full
throttle off load) for the first three tank fillings. This avoids
unnecessary high loads during the break-in period.
As all the moving parts have to bed in during the break-in
period, the frictional resistances in the engine are greater
during this period. For this reason the engine only de-
velops its maximum power after about 5 to 15 tank fillings.
The carburetor setting must never be made leaner in order
to achieve an apparent increase in power as this could
cause the engine to exceed its maximum permissible rpm
(see “Specifications” and “Carburetor”).
During operation
After a long period of working at full load it is advisable not
to shut off the engine immediately, but let it run for a short
while at idling speed. This allows the heat which has been
generated in the engine during full throttle operation to be
dissipated by the flow of cooling air and also protects
engine-mounted components (ignition, carburetor) from
thermal overload.
Spark plug
An incorrect carburetor setting, the wrong fuel mix (too
much engine oil in the gasoline), a dirty air filter and un-
favorable 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.
Top: Spark plug in good condition
Bottom: Spark plug fouled because of
incorrect running conditions
If the engine is down on power, difficult to start or runs
poorly at idling speed, check the spark plug before looking
any further. If the spark plug is dirty, clean it and check the
electrode gap. Readjust if necessary; the correct gap is
0.5 mm (0.02 in). The spark plug should be replaced after
about 100 operating hours or earlier if the electrodes are
badly eroded.
In order to ensure trouble-free operation it is necessary to
rectify the faults which have caused fouling of the spark
plug.