Stihl MS 261 C User manual

STIH)
STIHL MS 261 2010-05

1MS 261, MS 261 C
q
© ANDREAS STIHL AG & Co. KG, 2010
RA_573_0_01_02
1. Introduction and
Safety Precautions 3
1.1 Introduction 3
1.2 Safety Precautions 4
2. Specifications 5
2.1 Engine 5
2.2 Fuel System 5
2.3 Ignition System 5
2.4 Chain Lubrication 5
2.5 Tightening Torques 6
3. Troubleshooting 8
3.1 Clutch 8
3.2 Chain Drive,
Chain Brake,
Chain Tensioner 9
3.3 Chain Lubrication 11
3.4 Rewind Starter 12
3.5 Ignition System 14
3.6 Carburetor 15
3.7 Engine 18
4. Clutch 19
4.1 Clutch Drum 20
5. Chain Brake 21
5.1 Checking Operation 21
5.2 Brake Band 21
5.3 Brake Lever 23
5.4 Brake lever on
machines with
QuickStop Super 25
5.4.1 Adjusting the
brake cable 27
5.4.2 Brake cable 28
5.5 Cam Lever 29
5.6 Pins 30
5.7 Chain Tensioner 32
5.7.1 Quick chain tensioner 32
5.8 Bar Mounting Studs 33
5.9 Collar Nuts for
Sprocket Cover 34
6. Engine 35
6.1 Muffler 35
6.2 Leakage Test 36
6.2.1 Preparations 36
6.2.2 Vacuum Test 37
6.2.3 Pressure Test 37
6.3 Oil Seals 38
6.4 Shroud 39
6.5 Cylinder 40
6.6 Crankshaft 42
6.6.1 Bearings / Crankcase 47
6.7 Piston 48
6.8 Piston Rings 50
6.9 Decompression Valve 51
7. Ignition System 52
7.1 Ignition Timing 52
7.2 Preseparator 52
7.3 Install new
Ignition Module 52
7.4 Testing the
Ignition Module 54
7.5 Spark Plug Boot /
Ignition Lead 56
7.6 Flywheel 57
7.7 Short Circuit Wire 58
7.7.1 Testing 58
7.7.2 Removing and
Installing 58
7.7.3 Ground Wire 62
7.7.4 Contact Spring 62
7.8 Ignition System
Troubleshooting 64
8. Rewind Starter 67
8.1 General 67
8.2 Fan housing 67
8.3 Pawls 68
8.4 ErgoStart 69
8.5 Rope Rotor 70
8.6 Starter Rope / Grip 71
8.7 Tensioning the
Rewind Spring 73
8.8 Replacing the
Rewind Spring 73
9. Servicing the
AV System 76
9.1 Buffer on Oil Tank 76
9.2 AV Spring on
Oil Tank 76
9.2.1 AV Spring on Oil Tank -
Machines with
Heating 76
9.3 AV Spring on
Fuel Tank 77
9.4 AV Spring on
Handlebar 78
9.4.1 Models with Heating 79
9.5 Stop Buffer at
Clutch Side 79
9.5.1 Stop Buffer at
Ignition Side 80
9.5.2 Buffers on Filter Base 80
9.6 Handlebar 81
9.6.1 Handlebar with
Heating 82
10. Control Levers 87
10.1 Master Control Lever 87
10.1.1 Removing and
Installing 87
10.2 Throttle Trigger/
Lockout Lever 87
10.3 Throttle Trigger/
Lockout Lever –
QuickStop Super 89
10.3.1 Switch Lever –
QuickStop Super 91
10.3.2 Lockout Lever –
QuickStop Super 91
10.3.3 Choke Rod 92
10.3.4 Throttle Rod 93
11. Chain Lubrication 95
11.1 Pickup Body 95
11.2 Oil Suction Hose 95
11.3 Oil Pump 96
11.4 Valve 97
Contents

2MS 261, MS 261 C
Contents
12. Fuel System 98
12.1 Air Filter 98
12.2 Baffle 98
12.3 Filter Base 98
12.4 Air Guide Shrouds 100
12.4.1 Air Guide Shrouds –
Models with Manual
Fuel Pump 101
12.4.2 Air Guide Shrouds –
Models with Heating 104
12.5 Carburetor 109
12.5.1 Leakage Test 111
12.6 Servicing the
Carburetor 112
12.6.1 Metering Diaphragm 112
12.6.2 Inlet Needle 113
12.6.3 Pump Diaphragm 114
12.6.4 Levers on
Throttle Shaft 115
12.6.5 Adjusting Screws 116
12.7 Adjusting the
Carburetor 118
12.7.1 Basic Setting 118
12.7.2 Standard setting 119
12.8 Carburetor Carrier 120
12.9 Intake Manifold 121
12.10 Tank Vent 122
12.10.1 Testing 122
12.10.2 Removing and
Installing 123
12.11 Fuel Intake 123
12.11.1 Pickup Body 123
12.11.2 Fuel Hose 124
12.11.3 Fuel Hose – Models
with Manual Fuel
Pump 125
12.11.4 Manual Fuel Pump 127
12.11.5 Tank Housing 128
13. Heating System 130
13.1 Carburetor Heating 130
13.1.1 Testing the Complete
System 130
13.1.2 Testing the
Heating Element 130
13.1.3 Thermostatic Switch 131
13.2 Carburetor
Heating System
Troubleshooting
Chart 132
13.3 Handle Heating
System 133
13.3.1 Troubleshooting 133
13.4 Heater Switch 133
13.5 Heating Element
in Rear Handle 135
13.6 Heating Element
in Handlebar 136
13.7 Generator 137
13.7.1 Handle Heating and
Generator
Troubleshooting
Chart 139
13.7.2 Test Connections and
Test Values 141
13.8 Wiring Harness 143
14. Special Servicing
Tools 147
15. Servicing Aids 149

3MS 261, MS 261 C
1. Introduction and Safety Precautions
1.1 Introduction
This service manual contains
detailed descriptions of all the repair
and servicing procedures specific to
this power tool.
You should make use of the
illustrated parts lists while carrying
out repair work. They show the
installed positions of the individual
components and assemblies.
Refer to the latest edition of the
relevant parts list to check the part
numbers of any replacement parts.
A fault on the machine may have
several causes. To help locate the
fault, consult the troubleshooting
charts for all assemblies and
systems in this manual and the
"STIHL Service Training System".
Refer to the “Technical Information”
bulletins for engineering changes
which have been introduced since
publication of this service manual.
Technical information bulletins also
supplement the parts list until a
revised edition is issued.
The special tools mentioned in the
descriptions are listed in the chapter
on "Special Servicing Tools" in this
manual. Use the part numbers to
identify the tools in the "STIHL
Special Tools" manual. The manual
lists all special servicing tools
currently available from STIHL.
Symbols are included in the text and
pictures for greater clarity.
The meanings are as follows:
In the descriptions:
NAction to be taken as shown in
the illustration above the text
– Action to be taken that is not
shown in the illustration above
the text
In the illustrations:
APointer
aDirection of movement
@4.2 =Reference to another
chapter, i.e. chapter 4.2
in this example.
Service manuals and all technical
information bulletins are intended
exclusively for the use of properly
equipped repair shops. They must
not be passed to third parties.
Servicing and repairs are made
considerably easier if the machine
is mounted to assembly stand (3)
5910 890 3100. To do this, secure
the mounting plate (2)
5910 850 1650 to the assembly
stand with two screws (1) and
washers.
The screws must not project since
they, depending on the machine,
may damage housings when the
machine is clamped in position.
The above operation is not
necessary with the new assembly
stand 5910 890 3101 since the
mounting plate is already fitted.
Engage the bar mounting studs in
the outer bores in the mounting
plate and secure the machine in
position with the M 8 nuts (arrows).
1
2
3
219RA000 TG
5902RA000 TG

4MS 261, MS 261 C
Machines with Quick Chain
Tensioner
Engage the bar mounting stud in the
outer bore in the mounting plate and
secure the machine in position with
the M 8 nut (arrow).
The machine is held in position on
the mounting plate by the screw
heads on the engine housing.
Preparations for servicing
Remove the chain sprocket cover,
saw chain and guide bar before
carrying out repairs or mounting the
machine to the assembly stand.
Always use original STIHL
replacement parts.
They can be identified by the STIHL
part number, the
{
logo and the STIHL parts symbol
K
This symbol may appear alone on
small parts.
Storing and disposing of oils and
fuels
Collect fuel or lubricating oil in a
clean container and dispose of it
properly in accordance with local
environmental regulations.
5902RA001 TG
1.2 Safety Precautions
If the machine is started up in the
course of repairs or maintenance
work, observe all local and country-
specific safety regulations as well
as the safety precautions and
warnings in the instruction manual.
Gasoline is an extremely flammable
fuel and can be explosive in certain
conditions.
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.
Always wear suitable protective
gloves for operations in which
components are heated for
assembly or disassembly.
Improper handling may result in
burns or other serious injuries.
Do not smoke or bring any fire,
flame or other source of heat near
the fuel. All work with fuel must be
performed outdoors only. Spilled
fuel must be wiped away
immediately.
Always perform leakage test after
working on the fuel system and the
engine.
Always replace damaged parts.
Check disassembled parts for wear
or damage before re-installing –
replace as necessary.
Run the machine only with the
shroud mounted in position – there
is otherwise a risk of injury from the
fanwheel and a risk of engine
damage due to overheating.
The chapter on tightening torques
lists all machine components that
have to be tightened to a specific
torque or coated with threadlocking
adhesive. The specifications must
be maintained when tightening
down screws, nuts and other
fasteners in all the procedures
described in this service manual.
Fuel system – hose barb
connectors
Pull off or push on fuel hoses in line
with the connector, preferably by
hand, to ensure the tightness of the
fuel system.
Avoid damaging the hose barb
– do not use sharp-edged pliers,
screwdrivers, etc.
Do not cut open fuel hoses with a
knife or similar tool.
Do not re-use fuel hoses after
removal. Always install new hoses
– fuel hoses can be overstretched
during removal.
Install new fuel hoses either dry or
with the aid of STIHL press fluid,
b
b
15.
Other press fluids are not approved
and may result in damage to the fuel
hoses.
Coat the ends of the hoses and the
connectors with STIHL press fluid
and then push the new hoses on to
the hose barbs,
b
15.

5MS 261, MS 261 C
2. Specifications
2.1 Engine
MS 261
Displacement: 50.2 cm3
Bore: 44.7 mm
Stroke: 32.0 mm
Engine power to ISO 7293: 2.8 kW (3.8 bhp)
at 9,500 rpm
Maximum permissible engine speed
with bar and chain: 14,000 rpm
Idle speed: 2,800 rpm
Clutch: Centrifugal clutch without
linings
Clutch engages at: 3,600 rpm
Crankcase leakage test
at gauge pressure: 0.5 bar
under vacuum: 0.5 bar
2.2 Fuel System
Carburetor leakage test at
gauge pressure: 0.8 bar
Operation of tank vent at
gauge pressure: 0.5 bar
Fuel: as specified in instruction
manual
2.3 Ignition System
Air gap between ignition
module and fanwheel: 0.20 (+ 0.1/- 0.05) mm
Spark plug (resistor type): NGK BPMR 7 A
BOSCH WSR6F
Electrode gap: 0.5 mm
2.4 Chain Lubrication
Speed-controlled oil pump with reciprocating piston and
manual flow control
Settings for oil delivery rate:
min.:
Ematic
max.:
4.5 (+/2.0) cm3/min
at 10,000 rpm
8.5 (+/3.0) cm3/min
at 10,000 rpm
11.5 (+/3.0) cm3/min
at 10,000 rpm

6MS 261, MS 261 C
2.5 Tightening Torques
DG and P (Plastoform) screws are used in polymer and light metal components. These screws form a
permanent thread when they are installed for the first time. They can be removed and installed as often as
necessary without impairing the strength of the screwed assembly, providing the specified tightening torque is
observed.
For this reason it is essential to use a torque wrench.
Fastener Thread size For component Torque
Nm
Remarks
Screw P 4x12 Cover plate/sprocket cover (quick chain
tensioner)
2.5
Screw M 4x8 Chain tensioner cover plate/crankcase 2.0
Screw P 5x16 Antivibration spring / handle housing 3.0
Screw M 4x16 Antivibration spring / crankcase 3.5 4)
Screw M 4x12 Brake band/crankcase 3.0 1), 4)
Screw P 4x10 Brake cable retainer/ tank housing (Q) 1.7
Collar screw M 8 Collar stud for bar 23.0 1)
Collar screw M 8/M 10 Collar stud for bar (BE) 30.0 2)
Screw M 4x12 Cover, chain brake/crankcase 3.0 4)
M 10x1 Decompression valve 14.0
Screw M 4x9.6 Spark arresting screen/muffler 1.0
Screw M 12x0.75 Housing / switch (VW) 3.0
Screw M 4x12 Generator / crankcase (VW) 3.0 3)
Screw P 6x32.5 Handlebar/tank housing 7.0
Screw P 6x30 Handlebar / tank housing (VW) 8.0 4)
Screw M 6x26 Handlebar / bushing(VW) 8.0 2)
Screw M 5x16 Handlebar / plug, antivibration spring (VW) 6.0 3), 4)
Screw M 5x20 Hand guard/fan housing/crankcase 6.0 4)
Screw P 6x30 Chain catcher/crankcase/bearing plug 8.0
Screw M 5x16 Spiked bumper / crankcase / upper locknut 8.0 3), 4)
Lock nut M 5 Spiked bumper / crankcase / upper locknut 8.0
Screw M 5x16 Spiked bumper/crankcase, bottom 8.0 3), 4)
Screw M 4x12 Manifold/cylinder 3.0 4)
Screw M 5x25 Crankcase, sprocket side/fan side 10.0 4)
Screw M 5x16 Bearing plug/cylinder 10.0 3), 4)
Screw M 5x16 Fan housing/crankcase 6.0 4)
Screw M 4x12 Air baffle/crankcase 1.5 4)
Carrier M 12x1 L Carrier / crankshaft 50.0

7MS 261, MS 261 C
Fastener Thread size For component Torque
Nm
Remarks
Screw M 4x12 Oil pump/crankcase 3.0 4)
Screw M 5x16 Muffler/crankcase 10.0 3), 4)
Screw M 5x16 Muffler / cylinder 10.0 3), 4)
Nut M 8x1 Flywheel/crankshaft 28.0 5)
Screw M 4x12 Thermostatic switch / carburetor (VW) 2.0
Collar nut M 5 Carburetor / collar screw, 1st stage, fan side 2.0
Collar nut M 5 Carburetor / collar screw, 2nd stage, sprocket
side
3.5
Collar nut M 5 Carburetor / collar screw, 3rd stage, fan side 3.5
Screw M 5x16 Preseparator/crankcase 3.0 4)
M 14x1.25 Spark plug 25.0
Screw M 4x20 Ignition module/crankcase 4.0 3)
Screw M 5x20 Cylinder/crankcase, 1st stage 4.0 4)
Screw M 5x20 Cylinder/crankcase, 2nd stage 10.0 4)
Remarks:
1) Loctite 242 or 243, medium strength
2) Loctite 270, high strength
3) Micro-encapsulated screws
4) Screws with binding head
5) Degrease crankshaft/flywheel and mount oil-free
VW) Carburetor and handle heating system
Q) QuickStop Super
BE) Quick chain tensioner/ErgoStart
Use the following procedure when refitting a DG or P screw in an existing thread:
Place the screw in the hole and rotate it counterclockwise until it drops down slightly.
Tighten the screw clockwise to the specified torque.
This procedure ensures that the screw engages properly in the existing thread and does not form a new thread
and weaken the assembly.
Coat micro-encapsulated screws with medium strength Loctite 242 or 243 before reinstalling.
Power screwdriver setting for polymer: DG and P screws max. 500 rpm
Do not use an impact wrench for releasing or tightening screws.
Do not mix up screws with and without binding heads.

8MS 261, MS 261 C
3. Troubleshooting
3.1 Clutch
Condition Cause Remedy
Saw chain stops under full load Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Saw chain rotates at idle speed Engine idle speed too high Readjust idle speed screw LA
Clutch springs stretched Replace the clutch springs or install
new clutch
Clutch springs broken Replace the clutch springs
Loud noises Clutch springs stretched Replace all clutch springs
Needle cage damaged Fit new needle cage
Clutch shoe retainer broken Install new retainer or clutch
Clutch shoes and carrier worn Install new clutch

9MS 261, MS 261 C
3.2 Chain Drive, Chain Brake, Chain Tensioner
Condition Cause Remedy
Chain sprocket wears rapidly Chain not properly tensioned Tension chain as specified
Wrong chain pitch Fit chain of correct pitch
Insufficient chain lubrication Check chain lubrication
Saw chain stops under full load Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Brake band blocked Check freedom of movement and
operation of brake band
Saw chain rotates at idle speed Engine idle speed too high Readjust idle speed screw LA
Clutch springs stretched Replace the clutch springs or install
new clutch
Clutch springs broken Replace the clutch springs
Saw chain does not stop
immediately when brake is
activated
Brake spring stretched or broken Fit new brake spring
Brake band stretched or worn Fit new brake band
Clutch drum worn Install new clutch drum

10 MS 261, MS 261 C
Condition Cause Remedy
QuickStop Super
Coasting brake does not disengage
even though interlock lever is
depressed
Brake cable stretched Readjust brake cable
Brake cable disconnected or
broken
Reconnect or replace brake cable
QuickStop Super
Coasting brake does not disengage
properly even though interlock lever
is depressed
Too much free travel on interlock
lever
Adjust brake cable
QuickStop Super
Braking action of coasting brake
inadequate – interlock lever not
depressed
Brake cable overtensioned Adjust brake cable

11MS 261, MS 261 C
3.3 Chain Lubrication
In the event of trouble with the
chain lubrication system, check and
rectify other sources of faults
before disassembling the oil pump.
.
Condition Cause Remedy
Chain receives no oil Oil inlet hole in guide bar is blocked Clean oil inlet hole
Intake hose or pickup body clogged
or intake hose ruptured
Fit new intake hose and pickup
body
Valve in oil tank blocked Clean or replace valve
Teeth on worm worn Install new worm
Oil pump damaged or worn Install new oil pump
Machine losing chain oil Oil pump damaged or worn Install new oil pump
Oil suction hose connection
damaged
Install new oil intake hose
Gasket between two halves of
crankcase faulty or crankcase
cracked
Install new gasket, inspect both
halves of crankcase and replace if
necessary
Oil pump delivers insufficient oil Oil pump damaged or worn Install new oil pump
Oil pump delivery rate set too low Adjust oil pump
(only on version with adjustable oil
pump)
Worm driver is loose Install new worm

12 MS 261, MS 261 C
3.4 Rewind Starter
Condition Cause Remedy
Starter rope broken Rope pulled out too vigorously as
far as stop or over edge, i.e. not
vertically
Fit new starter rope
Normal wear Fit new starter rope
Starter rope does not rewind Rewind spring very dirty or
corroded
Clean or replace rewind spring
Insufficient spring tension Check rewind spring and increase
tension
Rewind spring broken Fit new rewind spring
Starter rope cannot be pulled out
far enough
Spring overtensioned Check rewind spring and reduce
tension
Starter rope can be pulled out
almost without
resistance (crankshaft does not
turn)
Guide pegs on pawls or pawls
themselves are worn
Fit new pawls
Spring clip on pawl fatigued Fit new spring clip
Spring clip installed wrong Install spring clip correctly
...Models with ErgoStart Torsion springs on flywheel
fatigued, pawls worn or sticking
Clean seats on pawls or replace
pawls and torsion springs if
necessary
Lugs on carrier worn Install new carrier
Spring loop in spring housing not
attached to carrier
Attach spring loop to carrier
Starter rope is difficult to pull –
models with ErgoStart
Spring in spring housing fatigued Install new spring housing

13MS 261, MS 261 C
Condition Cause Remedy
Starter rope is difficult to pull or
rewinds very slowly
Starter mechanism is very dirty Thoroughly clean complete starter
mechanism
At very low outside temperatures:
Lubricating oil on rewind spring
becomes viscous (spring windings
stick togteher) or moisture has got
onto the rewind spring (spring
windings frozen together)
Coat rewind spring with a small
amount of standard solvent-based
degreasant (containing no
chlorinated or halogenated
hydrocarbons), then pull rope
carefully several times until normal
action is restored

14 MS 261, MS 261 C
3.5 Ignition System
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
Ignition lead loose in ignition
module
Install new ignition lead
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
damaged or pole shoes have
turned blue
Install new flywheel
Ignition timing wrong, flywheel out
of adjustment
– key in flywheel has sheared off
Install new flywheel
Weak magnetization in flywheel Install new flywheel
Irregular spark Check operation of switch shaft/
contact spring 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.

15MS 261, MS 261 C
3.6 Carburetor
Condition Cause Remedy
Carburetor floods; engine stalls Inlet needle not sealing
– foreign matter in valve seat or
cone
Remove and clean the inlet needle,
clean the carburetor
Inlet needle worn Replace the inlet needle
Inlet control lever sticking on
spindle
Check the inlet control lever and
replace if necessary.
Helical spring not located on nipple
of inlet control lever
Remove the inlet control lever and
refit it correctly
Perforated disc on diaphragm is
deformed and presses constantly
against the inlet control lever
Fit a new metering diaphragm
Metered diaphragm deformed Fit a new metering diaphragm
Poor acceleration Setting of low speed screw too lean Check basic carburetor setting,
correct if necessary
Setting of high speed screw too
lean
Check basic carburetor setting,
correct if necessary
Inlet needle sticking to valve seat Remove inlet needle, clean and
refit
Diaphragm gasket leaking Fit new diaphragm gasket
Metering diaphragm damaged or
shrunk
Fit a new metering diaphragm
Tank vent faulty Replace tank vent
Leak on fuel hose from tank to
carburetor
Seal connections or install new fuel
hose
Engine loses power during
acceleration
Sealing ring or spring in accelerator
pump worn or damaged
Install new carburetor

16 MS 261, MS 261 C
Condition Cause Remedy
Engine will not idle, idle speed too
high
Throttle shutter opened too wide by
idle speed screw (LA)
Reset idle speed screw (LA)
correctly
Oil seals/crankcase leaking Seal or replace oil seals/crankcase
Throttle shutter does not close Install new carburetor
Engine stops while idling Idle jet bores
or ports blocked
Clean the carburetor
Low speed screw too rich or
too lean
Reset low speed screw (L)
correctly
Setting of idle speed screw LA
incorrect – throttle shutter
completely closed
Reset idle speed screw (LA)
correctly
Tank vent faulty Replace tank vent
Leak on fuel hose from tank to
carburetor
Seal connections or install new fuel
hose
Saw chain rotates at idle speed Engine idle speed too high Readjust with idle speed screw
LA (counterclockwise)
Clutch springs stretched or fatigued Replace the clutch springs or install
new clutch
Clutch spring hooks broken Replace the clutch springs

17MS 261, MS 261 C
Condition Cause Remedy
Engine speed drops quickly under
load – low power
Air filter dirty Clean air filter or replace if
necessary
Throttle shutter not opened fully Check throttle cable and rod
Tank vent faulty Replace tank vent
Fuel pickup body dirty Install new pickup body
Fuel strainer dirty Clean fuel strainer in carburetor,
replace if necessary
Leak on fuel hose from tank to
carburetor
Seal connections or install new fuel
hose
Setting of high speed screw Htoo
rich
Check basic carburetor setting,
correct if necessary
Main jet bores or ports blocked Clean the carburetor
Pump diaphragm damaged or
fatigued
Fit new pump diaphragm
Ignition timing wrong, flywheel out
of adjustment
– key in flywheel has sheared off
Install new flywheel
Engine running extremely rich, has
no power and a very low maximum
speed
Choke shutter does not open Check carburetor and choke shaft,
service or replace if necessary

18 MS 261, MS 261 C
3.7 Engine
Always check and, if necessary,
repair the following parts before
looking for faults on the engine:
- Air filter
- Fuel system
- Carburetor
- Ignition system
Condition Cause Remedy
Engine does not start easily, stalls
at idle speed, but operates normally
at full throttle
Oil seals in crankcase damaged Replace the oil seals
Crankcase leaking or
damaged (cracks)
Seal or replace the crankcase
Engine does not deliver full power
or runs erratically
Piston rings worn or broken Fit new piston rings
Muffler / spark arresting screen
carbonized
Clean the muffler (inlet and
exhaust), replace spark arresting
screen, replace muffler if necessary
Air filter dirty Clean or replace air filter
Fuel hose kinked or torn Fit new hose or position it free from
kinks
Decompression valve is not closed Close, check and replace
decompression valve if necessary
Engine overheating Insufficient cylinder cooling. Air
inlets in fan housing blocked or
cooling fins on cylinder very dirty
Thoroughly clean all cooling air
openings and the cylinder fins
Air flow path into fan housing dirty Clean air flow path into fan housing

19MS 261, MS 261 C
4. Clutch
– Troubleshooting,
b
3
– Remove the clutch drum,
b
4.1
– Remove the shroud,
b
6.4.
:Pull boot (1) off the spark plug.
– Unscrew the spark plug.
:Push the locking strip (1)
0000 893 5903 into the spark
plug hole, wide end first, so that
"OBEN-TOP" faces up.
5902RA002 TG
1
5902RA003 TG
1
:The locking strip (1)
0000 893 5903 must butt against
the cylinder wall (arrow) as
shown.
:Apply wrench to hexagon (arrow)
and unscrew the clutch (1).
Note that the clutch has a left-hand
thread.
Disassembling
:Use hook (2) 5910 890 2800 to
remove the clutch springs (1).
5902RA004 TG
1
off
off
off
5902RA005 TG
1
off
off
off
5902RA006 TG
21
If the clutch is noticeably worn,
replace all three clutch shoes at the
same time – not individual shoes –
since runout may otherwise affect
correct operation of the clutch.
:Fit the retainers (1).
:Fit the clutch shoes (2) over the
arms (1).
:Clamp the clutch in a
vise (arrow).
5902RA009 TG
1
off
5902RA010 TG
1 2
off
off
5902RA011 TG