Yamabiko ECHO SRM-420ES User manual

Ref. No. 402-44
ECHO: SRM-420ES SRM-420TES
T410S B410S
T410TS B410TS
shindaiwa:
(Serial number: 37000001 and after)
Copyright(C)2018 YAMABIKO Corporation All rights reserved.

INTRODUCTION
This service manual contains information for
service and maintenance of ECHO TRIMMER
/ BRUSHCUTTER, models SRM-420ES and
SRM-420TES, shindaiwa TRIMMER / BRUSH-
CUTTER, models T410S, B410S, T410TS and
B410TS.
For systematic diagnosis, to avoid extra work
and time loss, please refer to “Troubleshooting
guide” that describes problems, testings, reme-
dies and references. We recommend you make
use of Operator’s Manual and Parts Catalogue
together with this manual when servicing.
We are constantly working on technical improve-
ment of our products. For this reason, technical
data, equipment and design are subject to
change without notice. All specifications, illustra-
tions and directions in this manual are based on
the latest products information available at the
time of publication.

1
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS 1
TABLE OF CONTENTS
Page Page
1 SERVICE INFORMATION.....................................2
1-1 Specifications...................................................2
1-2 Technical data ..................................................4
1-3 Torque limits.....................................................5
1-4 Special repairing materials...............................5
1-5 Service Limits...................................................6
1-6 Special tools.....................................................7
2 STARTER SYSTEM..............................................8
2-1 Disassembling starter assembly.......................9
2-2 Replacing starter rope....................................10
2-3 Installing rewind spring...................................11
2-4 Assembling starter..........................................11
2-5 Replacing starter pawl....................................13
3 IGNITION SYSTEM.............................................14
3-1 Troubleshooting guide....................................14
3-2 Testing spark..................................................15
3-3 Inspecting spark plug .....................................15
3-4 Inspecting ignition switch................................16
3-5 Replacing ignition switch................................17
3-6 Inspecting ignition coil resistance...................21
3-7 Replacing spark plug cap and coil..................21
3-8 Replacing ignition coil.....................................22
3-9 Setting pole shoe air gaps..............................22
3-10 Inspecting flywheel and key ...........................23
4 FUEL SYSTEM ...................................................24
4-1 Inspecting air filter..........................................25
4-2 Inspecting fuel cap and fuel strainer...............25
4-3 Inspecting fuel tank and tank vent..................26
4-4 Replacing fuel line, fuel return line, tank vent
line and grommet............................................28
4-5 Adjusting carburetor.......................................30
4-5-1 General adjusting rules ..................................30
4-5-2 Throttle adjust screw, L mixture needle and
H mixture needle initial settings......................30
4-5-3 Adjusting carburetor.......................................31
4-6 Testing carburetor...........................................32
4-7 Inspecting crankcase pulse passage .............33
4-8 Inspecting metering lever height ....................33
4-9 Inspecting inlet needle valve..........................34
4-10 Inspecting diaphragm and others...................34
4-11 Replacing welch plug .....................................35
4-12 Replacing purge bulb .....................................35
4-13 Replacing throttle cable and control parts......36
4-14 Checking and adjusting throttle cable ............36
5 CLUTCH SYSTEM..............................................37
5-1 Removing clutch shoes and springs...............38
5-2 Installing clutch shoes....................................38
5-3 Removing clutch drum....................................39
5-4 Removing clutch drum bearings.....................39
5-5 Installing bearings and clutch drum................40
6 ENGINE...............................................................41
6-1 Testing cylinder compression.........................42
6-2 Cleaning cooling air passages .......................42
6-3 Inspecting muffler and exhaust port...............43
6-4 Testing crankcase and cylinder sealing..........44
6-5 Removing and inspecting cylinder..................44
6-6 Inspecting piston and piston ring....................45
6-7 Inspecting crankcase and crankshaft.............46
6-8 Replacing oil seal...........................................46
6-9 Replacing ball bearing....................................47
6-10 Assembling crankshaft and crankcase...........48
6-11 Installing piston...............................................48
6-12 Installing piston ring and cylinder...................49
7 CUTTER DRIVE SYSTEM..................................50
7-1 Replacing drive shaft......................................50
7-2 Disassembling gear case...............................51
7-3 Replacing gears and PTO shaft.....................52
7-4 Assembling gear case....................................54
8 MAINTENANCE GUIDE......................................55
8-1 Disassembly Chart.........................................55
8-2 Troubleshooting guide....................................56
8-3 Service Intervals.............................................58

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
2SERVICE INFORMATION 2
1 SERVICE INFORMATION
1-1 Specifications
Model SRM-420ES (L) SRM-420ES (U)
T410S B410S
Dimensions*1Length mm (in) 1840 (72.4)
Width mm (in) 355 (14.0) 700 (27.6)
Heigh mm (in) 287 (11.3) 585 (23.0)
Dry weight*2kg (lb) 7.8 (17.2) 8.5 (18.7)
Engine Type YAMABIKO, air-cooled, two-stroke, single cylinder
Rotation Counterclockwise as viewed from the output end
Displacement cm3 (in3) 41.5 (2.532)
Bore mm (in) 40.0 (1.575)
Stroke mm (in) 33.0 (1.299)
Compression ratio 6.7
Carburetor Type Rotary type : Diaphragm, horizontal-draft with purge bulb
Model WT-1046 WT-1046
WT-1170
Venturi size-Throttlebore mm (in) 12.7 - 14.3 (0.50 - 0.56)
Ignition Type CDI (Capacitor discharge ignition) system, Digital magneto
Spark plug BPMR8Y
Exhaust Muffler type Spark arrester muffler with catalyst
Starter Type ES-start (effortless) / Soft Start
Rope diameter x length mm (in) 3.8 x 910 (0.15 x 35.9)
Fuel*3Type*4Mixed two-stroke fuel
Mixture ratio 50 : 1 (2%)
Gasoline Minimum 89 octane
Two-stroke engine oil ISO-L-EGD (ISO/CD13738), JASO FC/FD
Tank capacity Full tank capacity: 0.69 (23.3)
L (U.S.fl.oz.) Usable capacity: 0.60 (20.3)
Clutch Type Centrifugal, 2-shoe pivot
Handle Type Front: Crescent loop with cushion
grip U-handle with integrated
control grip
Rear: Integrated control grip with
cushion
Drive shaft Type Solid type with serration (10-tooth)
Diameter - Length mm (in) 8.0 - 1588 (0.31 - 62.52)
Housing OD - ID mm (in) 28.0 - 24.0 (1.10 - 0.94)
(Main pipe) Length mm (in) 1537 (60.5)
Gear case Reduction ratio 1.33
Gear tooth Spiral bevel gear
Lubrication Lithium based grease
Cutter Type Nylon line cutter DS-5 3-tooth blade (255 mm)
Nylon line cutter DS-5
Arbor diameter for blade mm (in) 25.4 (1.0)
Fastener type, size mm Left-hand thread nut, M10 x 1.25 pitch
Cutting rotation Counterclockwise as viewed from top

3
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS SERVICE INFORMATION 3
1-1 Specifications (continued)
Model SRM-420TES (L) SRM-420TES (U)
T410TS B410TS
Dimensions*1Length mm (in) 1852 (72.8)
Width mm (in) 355 (14.0) 700 (27.6)
Heigh mm (in) 312 (12.3) 620 (24.4)
Dry weight*2kg (lb) 8.0 (17.6) 8.7 (19.2)
Engine Type YAMABIKO, air-cooled, two-stroke, single cylinder
Rotation Counterclockwise as viewed from the output end
Displacement cm3 (in3) 41.5 (2.532)
Bore mm (in) 40.0 (1.575)
Stroke mm (in) 33.0 (1.299)
Compression ratio 6.7
Carburetor Type Rotary type : Diaphragm, horizontal-draft, with purge bulb
Model WT-1046 WT-1046
WT-1170
Venturi size-Throttlebore mm (in) 12.7 - 14.3 (0.50 - 0.56)
Ignition Type CDI (Capacitor discharge ignition) system, Digital magneto
Spark plug BPMR8Y
Exhaust Muffler type Spark arrester muffler with catalyst
Starter Type ES-start (effortless) / Soft Start
Rope diameter x length mm (in) 3.8 x 910 (0.15 x 35.9)
Fuel*3Type*4Mixed two-stroke fuel
Mixture ratio 50 : 1 (2%)
Gasoline Minimum 89 octane
Two-stroke engine oil ISO-L-EGD (ISO/CD13738), JASO FC/FD
Tank capacity Full tank capacity: 0.69 (23.3)
L (U.S.fl.oz.) Usable capacity: 0.60 (20.3)
Clutch Type Centrifugal, 2-shoe pivot
Handle Type Front: Crescent loop with cushion grip U-handle with integrated
control grip
Rear: Integrated control grip with
cushion
Drive shaft Type Solid type with serration (10-tooth)
Diameter - Length mm (in) 8.0 - 1588 (0.31 - 62.52)
Housing OD - ID mm (in) 28.0 - 24.0 (1.10 - 0.94)
(Main pipe) Length mm (in) 1537 (60.5)
Gear case Reduction ratio 2.08
Gear tooth Spiral bevel gear
Lubrication Lithium based grease
Cutter Type Nylon line cutter B6
Arbor diameter for blade mm (in) 25.4 (1.0)
Fastener type, size mm Left-hand thread nut, M10 x 1.25 pitch
Cutting rotation Anticlockwise as viewed from top
OD: Outer diameter. ID: Inner diameter.
*1Without Nylon line head *2Without Nylon line head and Shield *3 Refer to Operator’s manual
*4Premixed alkylate fuel for 2-stroke can be used

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
4SERVICE INFORMATION 4
1-2 Technical data
Model SRM-420ES
T410S, B410S SRM-420TES T410TS, B410TS
Engine
Compression pressure MPa (kgf/cm2) (psi) 0.92 (9.4) (132)
Clutch engagement speed r/min 3,700
Ignition system
Spark plug gap mm(in) 0.6 - 0.7 (0.024 - 0.028)
Spark test Tester gap w/ spark plug mm(in) 4.0 (0.16)
Tester gap w/o spark plug mm(in) 6.0 (0.24)
Secondary coil resistance Ω930 - 970
Pole shoe air gaps mm(in) 0.3 - 0.4 (0.012 - 0.016)
Ignition timing at 3,000 r/min °BTDC 12
at 8,500 r/min °BTDC 29
Carburetor
Test Pressure, minimum MPa (kgf/cm2) (psi) 0.05 (0.5) (7.0)
Metering lever height mm(in) 1.65 (0.06) lower than diaphragm seat
Tool to adjust mixture needles D-shaped (L) P/N X645-000031
Carburetor adjustment
Cutting head preparation Nylon line cutter DS-5 B6
Line length*1190 mm without shield 240 mm without shield
1) Initial setting H mixture needle turn out 3
L mixture needle turn out 2 3/8
Throttle adjust screw turn in*22 1/8
Engine warm-up Idle - WOT : Total sec. 10 - 50 : 180
2) Find idle maximum speed Adjust L mixture needle to maximum idle speed*3
3) Set idle maximum speed w/ TAS r/min 3,550
4) Set idle speed
by turning L mixture needle CCW r/min 2,750
5) Find WOT maximum speed r/min Adjust H mixture needle to maximum WOT speed
6) WOT setting Turn H mixture needle CCW
to decrease WOT speed by : 120
r/min
7) Verify final engine speed with standard equipment Idle: 2,400 - 3,200
r/min WOT: 9,500 - 10,500*
WOT: 10,500 - 11,500** WOT: 9,800 - 11,000*
8) Verify clutch engagement speed Confirm clutch engagement speed.
If it is less than 1.25 times the idle speed, adjust
the idle speed by turning TAS CCW.
BTDC: Before top dead center. WOT: Wide open throttle CCW: Counterclockwise TAS: Throttle adjust screw
* With Nylon line head and shield ** With 3-tooth blade (255 mm)
*1From eyelet on nylon head
*2Set Throttle adjust screw to the point that its tip just contacts throttle plate before initial setting.
*3If clutch engages during adjustment process 2), decrease engine speed by turning TAS CCW until clutch
disengages and then redo 2).

5
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS SERVICE INFORMATION 5
1-3 Torque limits
Descriptions Size kgf•cm N•m in•lbf
Starter system Pawl M5 60 -90 6 -950
-80
Starter case M5*330 -45 3 -4.5 26 -40
Ignition system Magneto rotor (Flywheel) LM8 200 -240 20 -24 175 -210
Ignition coil M5 50 -70 5 -745
-60
Spark plug M14 130 -170 13 -17 115 -150
Fan cover M5 50 -70 5 -745
-60
Fuel system Carburetor M5 40 -55 4 -5.5 35 -50
Intake bellows M5*330 -50 3 -526
-45
Intake insulator M5*350 -70 5 -745
-60
Insulator plate M5*330 -45 3 -4.5 26 -40
Fuel tank bracket M5 50 -70 5 -745
-60
Fuel tank M5 50 -70 5 -745
-60
Clutch Clutch shoe M6 70 -110 7 -11 60 -95
Engine Crankcase M5*270 -110 7 -11 60 -95
Cylinder M5*270 -110 7 -11 60 -95
Cylinder cover M5*320 -30 2 -317
-26
Inner cylinder cover M5*330 -45 3 -4.5 26 -40
Stand M5*320 -30 2 -317
-26
Muffler M6 100 -140 10 -14 90 -125
Muffler cover M5*130 -45 3 -4.5 26 -40
Muffler stay M5 60 -90 6 -950
-80
Others Blade fastening nut LM10 280 -320 28 -32 245 -280
Regular bolt, nut, and screw M3 6 -10 0.6 -15
-9
M4 15 -25 1.5 -2.5 13 -22
M5 25 -45 2.5 -4.5 22 -40
M6 45 -75 4.5 -7.5 40 -65
M8 110 -150 11 -15 95 -130
M10 210 -300 21 -30 180 -260
LM: Left hand thread.
*1Apply thread locking sealant. (See “1-4 Special repairing materials”)
*2The torque differences among four bolts should not exceed 20 kgf•cm (2N•m, 17in•lbf) on one cylinder or
crankcase.
*3Precoat bolt: If old thread locking sealant is left in threads, correct torque may not be secured. In case old
thread locking sealant is left, remove it .
1-4 Special repairing materials
Material Location Remarks
Grease Gear case
Lithium based grease Rewind spring
Starter center post
Oil Oil seal inner lips Two-stroke engine oil or engine oil (SAE#30)Intake bellows lips
Drive shaft
Thread locking sealant Muffler cover Loctite #242, ThreeBond #1324 or equivalent
Ignition switch

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
6SERVICE INFORMATION 6
5K225 5K016 5K042
5K1895K219 5K220
5K246
5K245 5K223 5K2245K222
1-5 Service limits
ABCD
EFGH
KLM
Description mm (in)
A Cylinder bore When plating is worn and aluminum can be seen
BPiston outer diameter Min. 39. 91 (1.571)
CPiston pin bore Max. 10. 035 (0.3951)
DPiston ring groove Max. 1. 6 (0.063)
EPiston ring side clearance Max. 0. 1 (0.004)
FPiston pin outer diameter Min. 9. 98 (0.3929)
GPiston ring width Min. 1. 45 (0.057)
HPiston ring end gap Max. 0. 5 (0.02)
KCon-rod small end bore Max. 13. 025 (0.5128)
LCrankshaft runout Max. 0. 02 (0.001)
MClutch drum bore Max. 71. 5 (2.81)

7
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS SERVICE INFORMATION 7
Ignition Air Gap Gauge
#.014 = .35mm
P/N 91004
PET-304
Made in Germany
T27x200
4 0 1 0 5 5 7 8 6 9 7 4 5
0
1
2
3
4
5
6
7
1.35
0.4
1.65
1.5
1-6 Special tools
12345
7891012
15 16 17 18 19
20 21 23 24 25
11
6
13
Key Part Number Description Reference
1 X602-000340 Torx wrench (T27) Removing and installing torx bolt
2 PET304 Tachometer PET-304 Measuring engine speed to adjust carburetor
3 897800-79931 Spark tester Checking ignition system
4 91004 Module air gap gauge Adjusting pole shoe air gaps
5 V265-000200 Flange nut Removing crankshaft from crankcase (clutch side)
6 900100-08008 Bolt Removing crankshaft from crankcase (clutch side)
7 Y089-000111 Puller Removing magneto rotor
8 Y089-000094 Carburetor adjustment tool Adjusting carburetor
9 90101 Welch plug tool (ZAMA) Removing and installing welch plug
10 897563-19830 Metering lever gauge Measuring metering lever height on carburetor
11 X644-000020 Piston stopper Locking crankshaft rotation
12 91041 Pressure rubber plug Plugging exhaust port to test crankcase / cylinder leakages
13 897826-16131 Pressure rubber plug Plugging intake port to test crankcase / cylinder leakages
14 897827-16131 Pressure plate Plugging intake port to test crankcase / cylinder leakages
15 91149 Pressure / vacuum tester Testing crankcase and cylinder leakages
16 897803-30133 Pressure tester Testing carburetor and crankcase leakages
17 91037 Compression gauge Measuring cylinder compression
18 897701-14732 Bearing tool Removing and installing ball bearings on crankcase
19 897701-02830 Bearing wedge Removing ball bearings on crankshaft
20 897714-24330 Oil seal tool Installing ball bearings of gear case
21 10001-418430 Washer Installing crankcase oil seal
22 897726-21430 Oil seal tool Installing crankcase oil seal
23 897702-30131 Piston pin tool Removing and installing piston pin
24 897719-02830 Piston holder Making piston steady to remove and install piston/ring
25 P021-044870 PTO shaft puller Removing PTO shaft
14
22

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
8STARTER SYSTEM 8
2 STARTER SYSTEM (ES-Start / Soft start)
(A) Starter case
(B) Rewind spring
(C) Rope reel
(D) Power spring
(E) Pawl catcher
(F) Tapping screw
(G) Starter rope
(H) Starter grip
(C)
(B)
(D)
(d2)
(b)
(A)
(F)
(G)
(H)
(E)
Working principle
1. When starter grip (H) is pulled, rope reel (C) ro-
tates.
2. The rotation force of rope reel (C) is transmitted to
pawl catcher (E) by power spring (D) that is connect-
ed with rope reel (C) and pawl catcher (E).
3. Pawl catcher (E) engages with starter pawls on
flywheel to turn crankshaft.
4. The load from compression pressure in cylinder
will keep crankshaft from rotating as power spring (D)
is twisted and accumulates energy.
5. As starter grip (H) is pulled further, more energy
is stored in power spring (D) until the accumulated
energy is enough to overcome the compression
pressure in cylinder.
6. When accumulated energy in power spring (D)
overcomes the load from compression pressure in
cylinder, crankshaft is rotated.
7. Power spring (D) absorbs compression resistance
of cylinder and snatch back of engine during starting
action.
8. When starter rope (G) is released, rope reel (C)
is returned together with power spring (D) and pawl
catcher (E) by rewind spring tension.
9. After engine starts, starter pawls pivot outward by
centrifugal force and disengage from pawl catcher (E).
Construction
1. Rewind spring (B) is installed on rope reel (C).
2. Rope reel (C) with rewind spring (B) is installed
inside starter case (A).
3. Hook (a) located on the inside of starter case (A)
engages with end (b) of rewind spring (B).
4. Power spring (D) is installed on rope reel (C).
5. Hook of power spring (d2) engages with rope
reel (C) and top end hook (d1) of power spring
engages with pawl catcher (E).
(d1)
(a)

9
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS STARTER SYSTEM 9
2-1 Disassembling starter assembly
1. Remove stand (A).
2. Remove muffler cover (B) and cylinder cover (C).
3. Remove four bolts (D) and starter assembly (E)
from the unit.
4. Pull out starter rope about 30 cm (12 in) and
hold rope reel (F) by hand. Loop excess rope in
rope reel notch (f) as shown.
5. Rotate rope reel (F) clockwise to release tension
of rewind spring.
6. Remove tapping screw (G).
7. Remove pawl catcher (H) and power spring (J).
8. Remove rope reel (K) with rewind spring (L)
from starter case (M) slowly to prevent rewind
spring (L) from unwinding.
WARNING DANGER
Wear eye protection and take care when
removing rope reel. Rewind spring may un-
wind suddenly and cause personal injury.
K
G
JL
H
CB
E
M
A
D
f
F

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
10 STARTER SYSTEM 10
4. Make knot (D) at end of starter rope and pass
starter rope through hole of rope reel, then press
the knot (D) into recess as shown.
2-2 Replacing starter rope
1. Pull out and untie knot (A).
2. Pull knot (B) to remove rope from rope reel (C).
3. When installing new starter rope, singe both
ends of rope to prevent fraying.
5. Pass other end of starter rope through starter
case, from inside to outside.
6. Pass starter rope through starter grip. Make a
knot as shown.
7. Tighten knot. Push the knot into recess of starter
grip.
A
B
C
D
D

11
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS STARTER SYSTEM 11
2-3 Installing rewind spring
WARNING DANGER
Use of eye protection and safety gloves are
strongly recommended while working on re-
wind spring.
If rewind spring (A) is unwound from rope reel (B),
follow steps below.
1) Wind spring inside rope reel, hooking outer
hook (a) to holder (b) of rope reel (B) as shown.
2) Apply small amount of lithium based grease
to outside of rewind spring.
2-4 Assembling starter
3. Check for proper engagement of rewind spring
and rope reel by turning rope reel (A) clockwise
and counterclockwise.
A
ba
1. Lubricate center post (c2) of starter case with
lithium based grease.
2. Assemble rope reel (A) with rewind spring (B)
engaging hook (b1) with hook (c1) of starter case
(C).
B
A
A
b1
c1
B
C
c2

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
12 STARTER SYSTEM 12
4. Install power spring (D), engaging hook (d1) with
rope reel groove (a1).
5. Install pawl catcher (E), engaging hole (e) with
power spring top end hook (d2).
2-4 Assembling starter (continued)
D
d1
a1
eE
d2
6. Reinstall tapping screw (F) on starter post.
7. Pull out starter rope inside starter case. Rotate
rope reel counterclockwise several turns with start-
er rope hooked at notch (a2) as shown. Hold rope
reel to prevent it from rewinding and pull out starter
grip to take the rope slack.
a2
F
8. Pull starter several times to check rewind spring
tension. If starter is not rewinding fully, increase
spring tension by rotating rope reel one more turn
counterclockwise following above step (7).
9. Pull out starter rope all the way, and check that
rope reel can be rotated an additional half or more
turn counterclockwise as shown, to prevent rewind
spring from breaking.
10. If rope reel can not be turned counterclockwise,
reduce tension by rotating rope reel clockwise one
turn with starter rope hooked at notch (a2).

13
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS STARTER SYSTEM 13
2-5 Replacing starter pawl
1. Remove starter assembly from unit.
2. Loosen bolt (A) and remove washer (B), pawl (C),
and torsion spring (D). Replace damaged or worn
parts.
NOTE: When it is hard to loosen bolt, install piston
stopper X644-000020 (E) in spark plug hole to stop
crankshaft rotation and remove bolt easily.
3. Install torsion spring (D), pawl (C), washer (B)
and bolt (A). To avoid pinching of torsion spring,
install these parts without setting the end of torsion
spring (d1) on starter pawl.
4. Using fine wire (F) or appropriate tool, place the
end of torsion spring (d1) on pawl (B), by hooking
and passing under pawl as shown. Remove fine
wire or tool.
5. Make sure pawl can move smoothly. If it does
not move smoothly, check parts for correct installa-
tion.
D
C
B
A
E
d1
F
d1
B

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
14 IGNITION SYSTEM 14
3-1 Troubleshooting guide
3 IGNITION SYSTEM
(A) Flywheel
(B) Ignition coil
(C) Spark plug
(D) Spark plug cap coil
(E) Spark plug cap
(F) Spark plug cap cover
(G) High tension lead
(H) Primary leads
(J) Ground leads
(K) Ignition switch
(L) Woodruff key
(A)
(B)
(C)
(D)
(F)
(E)
(G)
(H)
(J)
Not
OK
Not
OK
Not
OK
OK
OK
OK
Spark plug
Spark
plug cap/
coil
Ignition
switch
Clean /
Regap /
Replace.
Replace.
Start
OK
OK
S.T.
Not
OK
S.T.
Not
OK
Not
OK
S.T.
OK
S.T.
Not
OK Pole
shoe air
gaps
Replace.
Not
OK OK
Not
OK
S.T.
OK
OK
Replace
ignition
coil.
Leads
connections
Not
OK
OK
OK
Not
OK
S.T.
Repair /
Replace.
Not
OK
Remedy
Inspect
Not
OK
Flywheel
key OK
R.T.*
End
Not
OK
Flywheel
magnet
Replace.
Not
OK
R.T.Not
OK
OK
OK
Replace ignition coil and / or inspect other
systems.
Replace flywheel.
OK
OK
Adjust pole shoe air gaps.
(Inspect flywheel magnet
at the same time. Go to
Aif OK.)
S.T.
Not
OK
A
S.T.: Spark test.
R.T.: Running test including actual cutting.
OK
OK
Secondary
coil
resistances
(L)
(K)

15
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS IGNITION SYSTEM 15
3K069
A
B
3-2 Testing spark
1. Remove spark plug cap from spark plug.
2. Connect spark plug cap to spark tester 897800-
79931 (A), and connect spark tester lead (B) on
spark plug as shown.
3. Screw in adjuster (a1) until the needle tips con-
tact. Turn out adjuster (a1) 4 turns to set spark
tester gap (a2) to 4 mm (0.16 in).
4. Turn ignition switch to “RUN” position. Pull start-
er grip several times.
5. If spark is steady in blue or white at the tester
gap, ignition system is considered good.
6. If no spark exists or spark is intermittent in
yellow, orange, or red, continue with further inspec-
tion.
WARNING DANGER
*Do not test near spark plug hole without
spark plug installed, otherwise there is a
chance to ignite fuel mixture inside cylinder.
*Do not touch metal parts of spark tester
while performing the test to avoid receiving
electrical shock.
*Do not check spark in area where gasoline
is spilled or flammable gases may exist.
3-3 Inspecting spark plug
1. Remove spark plug to inspect for fouling,
cracked or broken insulator, cracked outer elec-
trode, or rounded center electrode. Clean or
replace spark plug as required.
2. Set spark plug gap (A) by bending outer elec-
trode (B).
Standard : 0.6 to 0.7 mm (0.024 to 0.028 in)
NOTE: Take care not to crank outer electrode
when bending.
3. If engine does not start with correct spark plug,
inspect if spark plug is wet or dry. If it is excessive-
ly wet or dry, inspect fuel system.
GASO
LINE
a2
B
a1
A

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
16 IGNITION SYSTEM 16
3-4 Inspecting ignition switch
1. Disconnect primary lead coupler (A).
2. Disconnect ground lead coupler (B).
3. Connect one probe of Ohm-meter or multi-me-
ter to primary lead (C) of ignition switch side as
shown.
4. Connect other probe to ground lead (D) of igni-
tion switch side as shown.
5. When ignition switch is in “RUN” position, tester
should indicate infinite resistance.
6. When ignition switch is in “STOP” position, tes-
ter should show that circuit is in conducting state
(closed circuit).
7. If ignition switch is defective, replace with a new
one.
B
A
C
D

17
SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS IGNITION SYSTEM 17
3-5 Replacing ignition switch
Loop Handle type:
1. Disconnect primary lead coupler and ground
lead coupler (Refer to “3-4 Inspecting ignition
switch”). Disconnect throttle cable from carburetor.
Remove front handle .
2. Remove screws (A) and loosen screw (B). Re-
move main pipe from engine.
3. Loosen bolts (C) and slide cushion (D), harness
hanger (E) and handle fixture (F) to output end.
4. Remove screws (G) and remove rear handle
grip from drive shaft housing.
5. Disconnect end (h) of throttle
cable (H) from throttle trigger (J).
6. Remove throttle latch (K) with
torsion spring (M), throttle latch (N)
with torsion spring (P), throttle trig-
ger (J) with torsion spring (Q) and
throttle latch (R).
7. Remove ignition switch (S) with
leads, cushion (T), corrugated tube
(U) and throttle cable (H).
8. Pull out throttle cable from cush-
ion (T) and corrugated tube (U).
9. Pass throttle cable through
cushion (T) and corrugated tube
(U) of new ignition switch.
10. Route leads behind ignition
switch (S), and then install ignition
switch to rear handle grip half.
Route leads through grooves and
ribs of rear handle grip half as
shown.
C
A
B
D
CE
F
G
H
TU
N
S
P
R
J
h
Q
M
K
S

SRM-420ES, SRM-420TES
T410S, B410S
T410TS, B410TS
18 IGNITION SYSTEM 18
3-5 Replacing ignition switch (continued)
11. Set torsion spring (Q) to throttle trigger (J),
hooking one end of torsion spring to rib (j) of throt-
tle trigger as shown.
12. Set torsion spring (P) to throttle latch (N) as
shown.
13. Set torsion spring (M) to throttle latch (K),
hooking one end of torsion spring to rib (k) of throt-
tle latch as shown.
14. Install throttle latch (R). Install throttle trigger (J)
with torsion spring (Q), hooking torsion spring end
(q) as shown.
15. Install throttle latch (N) with torsion spring (P),
hooking torsion spring end (p) as shown. Install
throttle latch (K) with torsion spring (M), hooking
torsion spring end (m) as shown.
16. Connect end (h) of throttle cable (H) to throttle
trigger (J).
17. Install throttle cable (H), cushion (T) and
corrugated tube (U) to rear handle grip half as shown.
18. Install handle grip on drive shaft housing with
screws (refer to 4).
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. Install throttle tri
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