© STIHL Inc., Virginia Beach, VA     2013 US/STR
confidential
13. Spark Plug Appearance
Heavy 
carbon build-
up and oil 
fouled
Mix ratio 
incorrect.
Black, sooty 
appearance
Caused by 
rich fuel/air 
mixture
Normal color, 
normal electrode 
wear due to high 
run time
Normal color and 
wear
Carbon buildup 
due to high run 
time
Both of these 
plugs have served 
their useful life
© STIHL Inc., Virginia Beach, VA     2013 US/STR
confidential
14. Muffler
 Remove the 2 muffler nuts and 
deflector plate and inspect the 
spark arrester screen
 It must be present for all hand 
held engines used in the United 
States 
 The screen may be blocked 
with carbon deposits
 If necessary shine a light 
through the screen to verify