Stihl 38 User Guide

							FS 38
English
19
Remove the mowing head.
STIHL AutoCut
NHold the mowing head steady.
NUnscrew the cap counterclockwise.
STIHL PolyCut
NBlock the shaft.
NUnscrew the mowing head 
counterclockwise.This engine is certified to operate on 
unleaded gasoline and the STIHL two-
stroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of high-
quality gasoline and two-stroke air 
cooled engine oil.
Use mid-grade unleaded gasoline with a 
minimum octane rating of 89 ((R+M)/2) 
and no more than 10% ethanol content.
NOTICE
Fuel with an octane rating below 89 may 
increase engine temperatures. This, in 
turn, increases the risk of piston seizure 
and damage to the engine.
The chemical composition of the fuel is 
also important. Some fuel additives not 
only detrimentally affect elastomers 
(carburetor diaphragms, oil seals, fuel 
lines, etc.), but magnesium castings and 
catalytic converters as well. This could 
cause running problems or damage the 
engine. For this reason STIHL 
recommends that you use only quality 
unleaded gasoline!
NOTICE
Gasoline with an ethanol content of 
more than 10% can cause running 
problems and major damage in engines 
and should not be used.
For further details, see 
www.STIHLusa.com/ethanol
The ethanol content in gasoline affects 
engine speed – it may be necessary to 
readjust the carburetor if you use fuels 
with various ethanol contents.
WARNING
To reduce the risk of personal injury 
from loss of control and/or contact with 
the running cutting tool, do not use your 
unit with an incorrect idle adjustment. At 
correct idle speed, the cutting tool 
should not move.
If your machine’s idle speed is 
incorrectly adjusted, have your 
authorized STIHL servicing dealer 
check your machine and make the 
proper adjustments and repairs.
The idle speed and maximum speed of 
the engine change if you switch from a 
fuel with a certain ethanol content to a 
fuel with a much higher or lower ethanol 
content.
This problem can be avoided by always 
using fuel with the same ethanol 
content.
To ensure the maximum performance of 
your STIHL engine, use a high quality 2-
cycle engine oil. To help your engine run 
cleaner and reduce harmful carbon 
deposits, STIHL recommends using 
STIHL HP Ultra 2-cycle engine oil or ask 
your dealer for an equivalent fully 
synthetic 2-cycle engine oil. 
To meet the requirements of EPA and 
CARB we recommend to use STIHL HP 
Ultra oil.
STIHL MotoMix
STIHL recommends the use of STIHL 
MotoMix. STIHL MotoMix has a high 
octane rating and ensures that you 
always use the right gasoline/oil mix 
ratio.
Fuel 
						

							FS 38
English
20 STIHL MotoMix uses STIHL HP Ultra 
two-stroke engine oil suited for high 
performance engines.
For further details, see 
www.STIHLusa.com/ethanol
If not using MotoMix, use only STIHL 
two-stroke engine oil or equivalent high-
quality two-stroke engine oils that are 
designed for use in air cooled two-cycle 
engines.
The use of non-seasonal gasoline 
blends may increase the potential for 
pressure to build in the fuel tank during 
operation. For example, using a winder 
blend during the summer will increase 
pressure in the fuel tank. Always use 
gasoline blends appropriate to the 
season, altitude and other 
environmental factors.
Do not use BIA or TCW rated (two-
stroke water cooled) mix oils or other 
mix oils that state they are for use in both 
water cooled and air cooled engines 
(e.g., outboard motors, snowmobiles, 
chain saws, mopeds, etc.).
WARNING
Take care when handling gasoline. 
Avoid direct contact with the skin and 
avoid inhaling fuel vapor. When filling at 
the pump, first remove the container 
from your vehicle and place the 
container on the ground before filling. To 
reduce the risk of sparks from static 
discharge and resulting fire and/or 
explosion, do not fill fuel containers that 
are sitting in or on a vehicle or trailer.
The container should be kept tightly 
closed in order to limit the amount of 
moisture that gets into the mixture.The machine‘s fuel tank should be 
cleaned as necessary.
Fuel mix ages
If not using MotoMix, only mix sufficient 
fuel for a few days of work, not to exceed 
30 days of storage. Store in approved 
fuel-containers only. When mixing, pour 
oil into the container first, and then add 
gasoline. Close the container and shake 
it vigorously by hand to ensure proper 
mix of oil and gasoline.
Dispose of empty mixing-oil containers 
only at authorized disposal locations.Before fueling, clean the filler cap and 
the area around it to ensure that no dirt 
falls into the tank.
Always thoroughly shake the mixture in 
the canister before fueling your 
machine.
WARNING
In order to reduce the risk of fire and 
personal injury from escaping gas vapor 
and fumes, remove the fuel filler cap 
carefully so as to allow any pressure 
build-up in the tank to release slowly.
WARNING
After fueling, tighten fuel cap as securely 
as possible by hand. Gaso-
lineOil (STIHL 50:1 or equiva-
lent high-quality oils)
US gal. US fl.oz.
12.6
2 1/2 6.4
5 12.8
Fueling
232BA046 KN 
						

							FS 38
English
21
Controls
1Stop switch
2Throttle trigger lockout
3Throttle trigger
4Tongue of throttle trigger
5Catch
Positions of stop switch
6I – normal run position – the engine 
is running or can start
70 – Stop – engine off – the ignition is 
switched off
Starting
NMove the stop switch toI.
NPress down the throttle trigger 
lockout and hold it there.
NSqueeze the throttle trigger until the 
catch on the tongue (4) can be 
engaged on the housing (arrow).
NNow release the throttle trigger, 
tongue and trigger lockout in that 
order. This is the starting throttle 
position.NSet the choke lever (8) to
NPress the manual fuel pump 
bulb (9) at least five times – even if 
the bulb is filled with fuel.Starting / Stopping the 
Engine
2
232BA080 KN
167
54
3233BA047 KN
4
gif the engine is cold
efor warm start – also use this posi-
tion if the engine has been running 
but is still cold.
9
8
232BA011 KN 
						

							FS 38
English
22 Cranking
NPlace the unit on the ground: It must 
rest securely on the engine support 
and the deflector.
To reduce the risk of accidents, check 
that the cutting attachment is not 
touching the ground of any other 
obstacles.
NMake sure you have a firm footing, 
either standing, stooping or 
kneeling.
NHold the unit firmly on the ground 
with your left hand and press down 
– thumb under the fan housing – do 
not touch the throttle trigger or 
trigger lockout.
NOTICE
Do not stand or kneel on the drive tube.NHold the starter grip with your right 
hand.
NPull the starter grip slowly until you 
feel it engage and then give it a brisk 
strong pull.
NOTICE
Do not pull out the starter rope all the 
way – it might otherwise break.
NDo not let the starter grip snap back. 
Guide it slowly back into the housing 
so that the starter rope can rewind 
properly.
NContinue cranking.When engine begins to fire
NAfter no more than five pulls, move 
the choke lever (8) to e and
Ncontinue cranking.
As soon as the engine runs
NSqueeze the throttle trigger to 
disengage the tongue – the engine 
will settle down to idle speed.
WARNING
Make sure the carburetor is correctly 
adjusted. The cutting attachment must 
not rotate when the engine is idling.
Your machine is now ready for 
operation.
Stopping the Engine
NMove the stop switch to0. 
If engine does not start
Choke lever
If you did not move the choke lever 
quickly enough to e after the engine 
began to fire, the engine is flooded.
232BA012 KN
232TI013 KN
232BA014 KN
8
232TI015 KN 
						

							FS 38
English
23 NSet choke lever to e and
Nmove the stop switch to I, lockout 
lever and throttle trigger to the 
starting throttle position.
NStart the engine by pulling the 
starter rope briskly – 10 to 20 pulls 
may be necessary.
If the engine still does not start
NMove the stop switch to0.
NRemove the spark plug – see 
"Spark Plug".
NDry the spark plug.
NCrank the engine several times with 
the starter to clear the combustion 
chamber.
NRefit the spark plug – see "Spark 
Plug".
NMove the stop switch to I.
NSet choke lever to e – even if the 
engine is cold.
NNow start the engine.
Fuel tank run until completely dry
NAfter refueling, press the manual 
fuel pump bulb at least five times – 
even if the bulb is filled with fuel.
NSet the choke lever to suit the 
engine temperature.
NNow start the engine.
During break-in period
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 moving parts 
have to bed in during the break-in 
period, the frictional resistances in the 
engine are greater during this period. 
The engine develops its maximum 
power after about 5 to 15 tank fillings.
During Operation
After a long period of full throttle 
operation, allow the engine to run for a 
short while at idle speed so that engine 
heat can be dissipated by the flow of 
cooling air. This protects engine-
mounted components (ignition, 
carburetor) from thermal overload.
After Finishing Work
Storing for a short period: Wait for the 
engine to cool down. Empty the fuel tank 
and keep the machine in a dry place, 
well away from sources of ignition, until 
you need it again. For longer out-of-
service periods – see "Storing the 
Machine".If there is a noticeable loss of engine 
power
NSet the choke lever to g.
NPress in the tab (1) and swing the 
filter cover (2) down. 
NClean away loose dirt from around 
the filter.
Operating InstructionsCleaning the Air Filter
232BA017 KN
12 
						

							FS 38
English
24 NRemove the felt element (3) from 
the filter housing (4) and replace it – 
knock out or blow out as a 
temporary measure – do not wash.
NReplace damaged parts.
NFit the felt element (3) in the filter 
housing (4).
NClose the filter cover so that it snaps 
into position.Exhaust emissions are controlled by the 
design of the fundamental engine 
parameters and components (e.g. 
carburation, ignition, timing and valve or 
port timing) without the addition of any 
major hardware.
General Information
The carburetor comes from the factory 
with a standard setting.
This setting provides an optimum fuel-air 
mixture under most operating 
conditions.
Preparations
NShut off the engine.
NMounting the cutting attachment.
NCheck the air filter and clean or 
replace if necessary.
NCheck the spark arresting screen in 
the muffler and clean or replace if 
necessary. STIHL recommends that 
you have servicing and repair work 
carried out exclusively by an 
authorized STIHL servicing dealer.
232BA018 KN
4
3
(QJLQH0DQDJHPHQW$GMXVWLQJWKH&DUEXUHWRU 
						

							FS 38
English
25
Standard setting
NTurn high speed screw (H) 
counterclockwise as far as stop (no 
more than 3/4 turn).
NTurn the low speed screw (L) 
carefully clockwise as far as stop, 
then turn it back 3/4 turn.
Adjust idle speed
NCarry out the standard setting.
NStart and warm up the engine.
Engine stops while idling
NTurn the idle speed screw (LA) 
slowly clockwise until the engine 
runs smoothly – the cutting 
attachment must not rotate.Cutting attachment rotates when engine 
is idling
NTurn the idle speed screw (LA) 
counterclockwise until the cutting 
attachment stops moving and then 
turn the screw another 1/2 to 1 full 
turn in the same direction.
WARNING
If the cutting attachment continues to 
rotate when the engine is idling, have 
your machine checked and repaired by 
your servicing dealer.
Erratic idling behavior, poor acceleration 
(despite correction to setting of LA 
screw).
Idle setting is too lean
NTurn the low speed screw (L) 
carefully counterclockwise, no 
further than stop, until the engine 
runs smoothly and still accelerates 
satisfactorily.
Erratic idling behavior
Idle setting is too rich
NT u r n  t h e  l o w  s p e e d  s c r e w ( L )  s l o w l y  
clockwise, no further than stop, until 
the engine runs smoothly and still 
accelerates satisfactorily.
It is usually necessary to change the 
setting of the idle speed screw (LA) after 
every correction to the low speed 
screw (L).Fine Tuning for Operation at High 
Altitude
A slight correction of the setting may be 
necessary if engine does not run 
satisfactorily:
NCarry out the standard setting.
NWarm up the engine.
NTurn high speed screw (H) slightly 
clockwise (leaner) – no further than 
stop.
NOTICE
After returning from high altitude, reset 
the carburetor to the standard setting.
If the setting is too lean there is a risk of 
engine damage due to insufficient 
lubrication and overheating.
LH
LA
233BA050 KN 
						

							FS 38
English
26 If the engine is down on power, difficult 
to start or runs poorly at idling speed, 
first check the spark plug.
Install a new spark plug after approx. 
100 operating hours or earlier if the 
electrodes are badly eroded/corroded.
The 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 degrade performance.
Removing the Spark Plug
NMove the stop switch to0.
NPull off the spark plug boot (1).
NUnscrew the spark plug.
Checking the spark plug
NClean the spark plug if it is dirty
NCheck the electrode gap (A) and 
readjust if necessary – see 
"Specifications"
NUse only resistor type spark plugs of 
the approved range
Correct the problems that have caused 
fouling of the spark plug:
–too much oil in fuel mix,
–dirty air filter,
–unfavorable running conditions, e.g. 
operating at part throttle.
WARNING
T o  r e d u c e  t h e  r i s k  o f  f i r e  a n d  b u r n  i n j u r y ,  
use only spark plugs authorized by 
STIHL. Always press the spark plug 
boot (1) snugly onto the spark plug 
terminal (2).
Do not use a spark plug with a 
detachable SAE adapter terminal (3). 
Arcing may occur that could ignite 
combustible fumes and cause a fire. 
This can result in serious injuries or 
damage to property. 
NOnly use resistor type spark plugs 
with solid, non-threaded terminals
Installing the spark plug
NScrew home the spark plug, fit the 
boot and press it down firmly.
Spark Plug
1
232BA081 KN
000BA039 KNA
2
0000-GXX-1830-A0
3
1 
						

							FS 38
English
27 If engine running behavior is 
unsatisfactory even though the air filter 
is clean and the carburetor is properly 
adjusted, the cause may be the muffler.
Have the muffler checked for 
contamination (carbonization) by your 
servicing dealer.
STIHL recommends that you have 
servicing and repair work carried out 
exclusively by an authorized STIHL 
servicing dealer.For periods of about 3 months or longer
NDrain and clean the fuel tank in a 
well ventilated area.
NDispose of fuel properly in 
accordance with local 
environmental requirements.
NRun the engine until the carburetor 
is dry – this helps prevent the 
carburetor diaphragms sticking 
together.
NRemove, clean and inspect the 
cutting attachment.
NThoroughly clean the machine – pay 
special attention to the air filter.
NStore the machine in a dry and 
secure location – out of the reach of 
children and other unauthorized 
persons.
Placing power tool on the ground
NSwitch off the engine.
NLay your trimmer on its back with 
the loop handle and shroud pointing 
down and the output shaft facing up.
Replacing Nylon Line
Always check the mowing head for signs 
of wear before replacing the nylon line.
WARNING
If there are signs of serious wear, 
replace the complete mowing head.
The nylon mowing line is referred to as 
"nylon line" or "line" in the following.
The mowing head is supplied with 
illustrated instructions for replacing the 
nylon line. Keep the instructions for the 
mowing head in a safe place.
NIf necessary, remove the mowing 
head.
Engine Running BehaviorStoring the MachineMaintaining the Mowing 
Head
546BA016 KN 
						

							FS 38
English
28
Adjusting Nylon Line
STIHL AutoCut
NHold the rotating mowing head 
above the ground – tap it on the 
ground once – about 3 cm (1.2 in) of 
fresh line is advanced.
NThe blade (1) on the deflector (2) 
trims surplus line to the correct 
length – avoid tapping the mowing 
head more than once at a time.
Line feed operates only if both lines still 
have a minimum length of 2.5 cm (1 in).
If the line is shorter than 2.5 cm (1 in):
WARNING
To reduce the risk of injury, always shut 
off the engine before adjusting the nylon 
mowing line by hand.NTurn the machine over.
NPress down the cap on the spool as 
far as stop.
NPull the ends of the lines out of the 
spool.
If the spool is empty, refill with nylon line.
All other mowing heads
Refer to the leaflet supplied with the 
mowing head.
WARNING
To reduce the risk of injury, always shut 
off the engine before adjusting the nylon 
mowing line by hand.
Replacing Nylon Line
STIHL DuroCut
WARNING
To reduce the risk of injury, always shut 
off the engine before refilling the mowing 
head.
NFit nylon line in the mowing head as 
described in the instructions 
supplied.
STIHL AutoCut C 5-2
Disassembling the mowing head and 
removing remaining nylon line
In normal operation, the supply of nylon 
line in the head is used up almost 
completely.NHold the mowing head steady and 
rotate the cap (1) counterclockwise 
until it can be removed.
NPull the spool (2) out of the mowing 
head (3) and remove the remaining 
line.
1
232BA007 KN
2
Schnur/LINE  1
681BA021 KN
1
2
3