Stihl MS 171 Manual page 13

4.5 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
Engine runs roughly, misfires,
temporary loss of power
A problem with the carburetor or the engine can also be the reason for erratic running behavior.
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Cause
Spark plug boot is loose
Spark plug sooted, smeared
with oil
Fuel/oil mixture
– too much oil
Incorrect air gap between ignition
module and flywheel
Flywheel cracked or has other
damage or pole shoes have turned
blue
Ignition timing wrong, flywheel out
of adjustment, key in flywheel has
sheared off
Weak magnetization in flywheel –
pole shoes have turned blue
Irregular spark
Remedy
Press boot firmly onto spark plug
and fit new spring if necessary
Clean the spark plug or replace if
necessary
Use correct mixture of fuel and oil
Set air gap correctly
Install new flywheel
Install new flywheel
Install new flywheel
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 spark plug and replace if
necessary.
MS 171, MS 181, MS 211