Stihl FS 40, Service Manual

Page: 10 / 82

9 Series 4144 Components FC, FS, KM
4.3 Ignition System
Exercise extreme caution while
carrying out maintenance and
repair work on the ignition system.
The high voltages which occur can
cause serious or fatal accidents.
Condition Cause Remedy
Engine runs roughly, misfires,
temporary loss of power Spark plug boot is loose Press boot firmly onto spark plug
and fit new spring if necessary
Spark plug sooted, smeared with oil Clean the spark plug or replace if
necessary.
If sooting keeps recurring, check air
filter
Fuel/oil mixture
– too much oil Use correct mixture of fuel and oil
Incorrect air gap between ignition
module and flywheel Set air gap correctly
Flywheel cracked or has other
damage or pole shoes have turned
blue Install new flywheel
Ignition timing wrong, flywheel out
of adjustment, key on crankshaft
has sheared off Locate flywheel properly or install
new flywheel
Weak magnetization in flywheel Install new flywheel
Irregular spark Check operation of switch shaft/
contact springs and ignition
module.
Faulty insulation or break in ignition
lead or short circuit wire. Check
ignition lead/ignition module and
replace ignition module if
necessary.
Check operation of spark plug.
Clean the spark plug or replace if
necessary.
Crankcase damaged (cracks) Install new crankcase