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User Manual: Redmax Redmax-Gz25N-Workshop-Manual-822458
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STRATO CHARGED ENGINE
GZ25N
R
Workshop Manual
July 2000
S4810-0006
Applicable Model Name:
1. Brushcutters BCZ2500S/BCZ2500SU
2. Long Reach Trimmer LRTZ2500
3. Short Reach Trimmer SRTZ2500
4. Pole Saw PSZ2500
5. Reciprocator SGCZ2500S
6. Sweeper RMSZ2500
7. Hand Held Edger HEZ2500S
8. Split Boom Trimmer : EXZ2500S
3
BRUSHCUTTERS
BCZ2500S/BCZ2500SU
CONTENTS
1. OUTLINE OF STRATO-CHARGED ENGINE .................................
2
1-1 Special Features ................................................................................................................................. 2
1-2 Principle of Operation ......................................................................................................................... 3
1-3 Construction (Developed Drawing) ..................................................................................................... 4
2. SPECIFICATIONS AND TECHNICAL DATA ..................................
5
3. OUTLINE DRAWING ......................................................................
6
4. MAINTENANCE SPECIFICATIONS ...............................................
7
4-1 Engine Block ....................................................................................................................................... 7
4-2 Carburetor .......................................................................................................................................... 8
4-3 Ignition System ................................................................................................................................... 8
4-4 Fastening Specifications ...................................................................................................................... 8
4-5 Sealant and Lubricant Specifications .................................................................................................. 8
5. SPECIAL TOOLS ............................................................................
9
6. SERVICE GUIDE ..........................................................................
10
6-1 GENERAL PRECAUTIONS .............................................................................................................. 10
6-2 Removing of Clunch Shoe ............................................................................................................... 11
6-3 Mounting of Clutch Shoe ................................................................................................................... 11
6-4 Removing of Rotor ............................................................................................................................ 11
6-5 Removing Recoil Pulley .................................................................................................................... 12
6-6 Assembling of lgnition Coil ................................................................................................................ 12
6-7 Installing of Spark Plug .................................................................................................................... 12
6-8 Laying of Switch Cable .................................................................................................................... 13
6-9 Fitting of Plug Cap ............................................................................................................................ 13
6-10 Removing Piston Pin ......................................................................................................................... 13
6-11 Installing of Piston 14
6-12 Assembling of Piston Pin Circlip ........................................................................................................ 14
6-13 Direction of Setting Cylinder Gasket ................................................................................................. 14
6-14 Positioning of Lead Air Intake Tube .................................................................................................... 15
6-15 Assembling of Cylinder Plate ............................................................................................................. 15
6-16 Setting of Insulator Gasket ................................................................................................................. 15
6-17 Mounting of Reed Valve ..................................................................................................................... 16
6-18 Removal of Clutch Drum .................................................................................................................... 16
6-19 Assembling Cluch Drum .................................................................................................................... 17
7. CARBURETOR .............................................................................
18
7-1 Construction ..................................................................................................................................... 18
7-2 Function and Operation of Throttle Valve .......................................................................................... 18
7-3 Specifications .................................................................................................................................... 19
7-4 Composition and Inspection .............................................................................................................. 20
8. TROUBLE SHOOTING .................................................................
21
8-1 Engine does not start ........................................................................................................................ 21
8-2 Stalled during Operation ................................................................................................................... 21
8-3 Engine cannot be stopped ................................................................................................................ 22
8-4 Lack of output power or unstable revolution ..................................................................................... 22
1-1 Special Features
Unlike the conventional 2-stroke engine scavenging system, the Strato-charged Engine scavenges burnt gas by the stratified lead air scavenging method.
By creating a stratified air layer between burnt gas and the air-fuel mixture, this system significantly reduces exhaust of unburned air-fuel mixture.
Difference to the conventional 2-stroke engine is its very simple construction applying a new carburetor for independent intake of the air and the air-fuel mixture, an insulator, lead air intake tubes, and reed valves, etc.
Carburetor
Insulator Lead Air Intake Tube (each side)
Reed Valve (each side)
2
By the stratified lead air scavenging system, the Strato-charged Engine reduces
unburned air-fuel mixture exhaust to about 1/3 of the conventional 2-stroke engine
level.
By optimizing the combustion chamber design, ignition plug position, and ignition
timing, lean burn operation became possible.
By combining with the stratified lead air scavenging system, pollutant contained in the
exhaust was reduced and fuel consumption was reduced by 30% without reducing the
power.
As the catalytic converter is not applied, exhaust gas temperature increase due to the
catalytic reactive heat does not occur so that the engine heat load does not increase.
Therefore, same level of durability and reliability with the conventional engines are
assured.
A large size silencer and a muffler were employed and the noise level was reduced by
5 dB(A) compared to the conventional 2-stroke engines.
STRATO CHARGED ENGINE
GZ25N
1. OUTLINE OF STRATO-CHARGED ENGINE
Unit : g/HP•h (g/kwh)
THC + NOx CO PM
171.2
(232)
280
(381)
139.1
(189) 5.3
(7.2)
1.5
(2.0) 1.0
(1.3)
400
(544)
54
(73) 49.5
(67)
Current Engine
Tier 2 regulation
Strato-Changed Engine
3
STRATO CHARGED ENGINE
GZ25N
1. OUTLINE OF STRATO-CHARGED ENGINE
1-2 Principle of Operation
Major difference of the Strato-charged Engine to the conventional 2-stroke engine is that as illustrated on the following drawing, there are lead air intake tubes which are connected to the scavenging port via reed valves.
Lead Air Intake Tube
Reed Valve Assy
Carburetor
Air-Fuel Mixture
Scavenging Port
Scavenging Port
Reed Valve
Air
Lead Air
Burnt Gas
Exhaust Port
Due to crankcase depression during the piston upstroke
(intake stroke) to the top dead centre, air-fuel mixture is charged
to the crankcase and lead air is charged to the scavenging
ports though the reed valves.
As piston proceeds to downstroke after the top dead center,
a scavenging port starts to open and lead air in the scavenging
port moves into the cylinder earlier than the air-fuel mixture.
As piston proceeds to upstroke after the bottom dead center,
burnt gas in the cylinder is pushed out through the exhaust
port by lead air. Therefore, direct exhaust of air-fuel mixture
is almost non.
Lead Air
Crankcase
Air-Fuel Mixture
Air
Air-Fuel Mixture
Air-Fuel Mixture
Lead Air
Burnt Gas
Exhaust Port
Air-Fuel Mixture
4
STRATO CHARGED ENGINE
GZ25N
1. OUTLINE OF STRATO-CHARGED ENGINE
1-3 Construction (Developed Drawing)
Parts in the frames are exclusively designed for the Strato-charged Engine.
Spark Plug
Cylinder
Reed Valve
Reed Valve
Carburetor
Lead Air Intake Tube
Lead Air Intake Tube
Insulator
• Brushcutters BCZ2500S/BCZ2500SU
• Long Reach Trimmer LRTZ2500
• Short Reach Trimmer SRTZ2500
• Pole Saw PSZ2500
• Sweeper RMSZ2500
• Hand Held Edger HEZ2500S
• Split Boom Trimmer : EXZ2500S
• Reciprocator SGCZ2500S
5
STRATO CHARGED ENGINE
GZ25N
2. SPECIFICATIONS AND TECHNICAL DATA
Item Unit Specifications Remarks
Engine GZ25N
Engine Type Air cooled 2-stroke single cylinder
piston valve gasoline engine
Cylinder Bore x Stroke mm (in.) ø34 x 28 (1.339 x 1.102)
Displacement cc (cu.in.) 25.4 (1.6)
Effective Compression Ratio 8.0
Fuel
Mixture of 87 octane or above unleaded
Use JASO FC
gasoline and RedMax 2-cycle engine oil
or ISO EDG
(ratio 50 :1) or quality oil for air cooled grade 2-cycle
2-cycle engines (ratio 32:1). engine oil.
Carburetor Type Diaphragm Rotary valve
Model Walbro WYA-1B
Starting Method Recoil starter
Ignition System CDI with automatic timing advance
system.
Ignition Timing °/ rpm 35 / 7000
Spark Plug NGK CMR7A
Stopping Method Primary coil short-circuiting
Cooling System Forced Air Cooling
Air Cleaner Dry Type
Output Axle Rotation Direction
Counterclockwise (View from
PTO)
Clutch Type Automatic Centrifugal Clutch
(Sintered Clutch Shoe)
Overall Size
Engine GZ25N
for
Engine GZ25N2 for
exept SGCZ2500S SGCZ2500S
Length mm (in.) 271 (10.67) 188 (7.40)
Width mm (in.) 223 (8.78) 223 (8.78)
Height mm (in.) 248（9.76）248（9.76）
Dry Weight kg (lbs.) 3.1（6.8）2.8（6.2）
Fuel tank Capacity lit. (fl,oz) 0.65（22.0）
Operating Speed rpm 6000 10000
Idling Speed rpm 3000 ±200
Clutch Engagement Speed rpm 4000 ±200
No-Load Max Speed rpm 10000 With Standard
Head
Max Output HP(kW) / rpm 1.2 (0.9) / 7500
Max Torque kg•m(in.lbs) / rpm 0.12 (10.4) / 6500
Full Load Fuel Consumption g/HP.h(g/kW.h) 330 (449)
6
STRATO CHARGED ENGINE
GZ25N
3. OUTLINE DRAWING
Unit : mm (in.)
Engine Cover
Muffler
Tank Guard
Fuel Tank
Fuel Cap
Air Cleane
Carburetor
Plug Cap
Recoil Starter
Fan Cover
Fan Cover
122 (4.80)
223 (8.78)
168 (6.61)
238 (9.36)
271 (10.67)
85 (3.35)
7.85
(0.31)
155 (6.10)
188 (7.40)
113 (4.45)
248 (9.76)
113 (4.45)
248 (9.76)
GZ25N for
BCZ2500S, BCZ2500SU,
LRTZ2500, SRTZ2500,
PSZ2500, RMSZ2500,
HEZ2500S and EXZ2500S.
GZ25N2 for
SGCZ2500S.
7
STRATO CHARGED ENGINE
GZ25N
4. MAINTENANCE SPECIFICATIONS
4-1 Engine Block
Cylinder
Compression 8.7(124) 5.5(78) Compression
kg/cm
2
(psi) Gauge
Bore ø34(1.339)
Peel off of plating or
Cylinder
mm(in.)
expose of base met Gauge
Piston
Piston dia.
ø33.96(1.3370)
ø33.86(1.3331) Micrometer At right angle to
mm(in.)
ø33.975(1.3376)
piston pin.
Piston Ring Groove Width mm(in.)
1.2(0.047) 1.3(0.051)
Thickness Gauge
Piston Pin Hole Bore mm(in.)
ø8(0.3150) ø8.04(0.3165)
Cylinder Gauge
Clearance between
0.025(0.0010)
0.15(0.0059) Micrometer /
Piston & Cylinder mm(in.)
0.065(0.0026)
Cylinder Gauge
Clearance between Groove
0.04 (0.0016)
0.1(0.0039) Thickness
and Piston Ring
mm(in.)
0.08(0.0031)
Gauge
Fitting between Piston Pin &
0.005T(0.00020T)
0.05L(0.0020L) Micrometer /
Piston Pin Hole
mm(in.)
0.011L(0.00043L)
Cylinder Gauge
Piston Ring
End Gap
mm(in.)
0.1(0.0038) 0.5(0.0197)
Thickness Gauge
Measure at
0.3(0.0118 cylinder skirt.
Width
mm(in.)
1.2(0.0472) 1.1(0.0433) Micrometer
Piston Pin
Diameter
mm(in.)
ø8(0.315) ø7.98(0.314) Micrometer
No stepwear is allowed
Connecting Rod
Small End Bore
mm(in.) ø11
(0.433) ø11.05(0.435)
Cylinder Gauge
Clearance between Small End Piston 0 0.021(0.0008)
0.045(0.0018) Micrometer /
Pin & Needle Bearing mm(in.)
Cylinder Gauge
Clearance between Large End Crank 0.005(0.0002)
0.05(0.0020) Micrometer /
Pin & Needle Bearing
mm(in.)
0.028(0.0011)
Cylinder Gauge
Parallelness of Large/Small – 0.15/100 Mandrel
End Bores
mm(in.)
Dial Gauge
Crankshaft
Diameter at Main Bearing ø12(0.4724) ø11.97(0.4713) Micrometer
(MAG, PTO)
mm(in.)
Diameter at Oil Seal ø12(0.472) ø11.09(0.469) Micrometer
(MAG, PTO)
mm(in.)
Diameter at Clutch Drum ø12(0.4724) ø11.97(0.4713) Micrometer
Bearing ( PTO)
mm(in.)
Eccentricity
mm(in.)
– 0.07(0.028) Dial Gauge /
Adjust or exchange
Centre Support
Width between crank webs mm(in.)
22 21.9 22.1 Micrometer
Axial Play
mm(in.)
– 0.5(0.020)
Thickness Gauge
Main Bearing (Ball Bearing) –Flutter, irregular
noise generated
Clutch Drum
Bore at Bearing
mm(in.)
ø12 (0.472) ø12.05(0.474)
Cylinder Gauge
Bore at Drum
mm(in.)
ø54(2.126) ø54.6(2.150)
Vernia Calipers
Maintenance Item
Standard
Limit
Remarks
Measuring
Instrument
8
STRATO CHARGED ENGINE
GZ25N
4-2 Carburetor
4-3 Ignition System
4-5 Sealant and Lubricant Specifications
Carburetor WYA-1B
Metering Lever set. mm.(in.) 1.5 (0.059) ±0.16 (±0.006) Vanier
Inlet valve opening pressure. kg/cm2(p.s.i)
1.5 (21.3) ±0.5 (±7.1) Leak Tester
Inlet valve reseating pressure. kg/cm2(p.s.i)
0.9 (12.8) ±0.5 (±7.1) Leak Tester
Remarks
Maintenance Item Standards Limit Measuring
instrument
4-4 Fastening Specifications
Electric parts
Spark plug air gap. mm.(in.) 0.6 0.7 0.7 (0.028) Vanier
(0.025 0.028)
Ignition coil air gap. mm.(in.) 0.3 (0.012) 0.4 (0.016) Air gap gauge
Ibnition coil resistance
Primary side Ohm
2300 Volt Meter Reading between primary terminal
and iron core.
Secondary side Ohm
1100 Volt Meter Reading between high tension
terminal and iron core.
Remarks
Maintenance Item Standards Limit Measuring
instrument
AREA MATERIAL TO BE APPLIED
Recoil spring Grease
Reel center hub Grease
Recoil Starter:
AREA MATERIAL TO BE APPLIED
Sliding portion Grease
of screw.
Clutch:
AREA MATERIAL TO BE APPLIED
Oil seal lip Grease
Piston sliding area 2-cycle oil
Main bearing 2-cycle oil
Piston pin bearing 2-cycle oil
Crank pin bearing 2-cycle oil
Engine Block:
4. MAINTENANCE SPECIFICATIONS
Standard fix torque
Carburetor Fix Bol M5 (P=0.8) 38(33) 30(26) 45(39)
Insulator Fix Bolt M5 (P=0.8) 45(39) 40(35) 55(48)
Clutch M5 (P=1.0) 65(56) 50(43) 80(69)
Rotor Fix Nut M8 (P=1.0) 130(112) 100(87) 150(130)
Cylinder Fix Bolt M5 (P=0.8) 70(61) 60(52) 80(69)
Crankcase Fix Bolt M5 (P=0.8) 65(56) 50(43) 80(69)
Grass Guard Fix Bolt M5 (P=0.8) 38(33) 30(26) 45(39)
Spark Plug M10 (P=1.0) 110(96) 100(87) 120(104)
Muffler Fix Bolt M5 (P=0.8) 90(78) 70(61) 100(87)
Engine Cover Fix Bolt M5 (P=0.8) 38(33) 30(26) 45(39)
Fan Cover Fix Bolt M5 (P=0.8) 38(33) 30(26) 45(39)
Ignition Coil Fix Bol M4 (P=0.7) 33(29) 25(22) 40(35)
Recoil Starter Fix Bolt M5 (P=0.8) 38(33) 30(26) 45(39)
Recoil Pulley M8 (P=1.25) 90(78) 80(69) 100(87)
Fuel Tank Fix Bolt M5 (P=0.8) 38(33) 30(26) 45(39)
Common fixing torque
Tapping Screw TP4.3 10 (9) 7(6) 15(13)
TP5.4 25(22) 20(17) 30(26)
Screw Lock Agent
Fixing Components Screw Size Fixing torque
Target Tolerance
Unit : kg
.
cm(in.lbs)
9
STRATO CHARGED ENGINE
GZ25N
5. SPECIAL TOOLS
Part name Part No. External appearance Usage
4
Air Gap Gauge 3350-96240 To set ignition coil.
To remove / install piston
pin.
3
Rod Assy 1101-96220
To hold crankshaft when
disassembling /
assembling clutch and
rotor.
2
Piston Stopper 4810-96220
1
Puller Assy 2890-96100 To remove rotor.
8
Drum Remover 5500-96120 To remove clutch drum.
9
Snap Ring Guide
5500-96130 To install clutch drum.
10
Snap Ring Push 5500-96140 To install clutch drum.
Guide
For socket screw of
Hex.3mm,4mm and 5mm.
5
Hex Wrench 3304-97611
To remove / install recoil
pulley
6
Puller 4500-96100
7
Snap Ring Pliers
5500-96110 To remove snap ring.
10
STRATO CHARGED ENGINE
GZ25N
6. SERVICE GUIDE
6-1 GENERAL PRECAUTIONS
■Before beginning repair work
Check each system thoroughly before beginning repair work. Inspect from the point where it is simplest and
easiest for trouble to occur.
Step-by-step inspection in the following order is recommended.
Ignition system: From electric output(spark plug) to electric input(ignition coil).
Fuel system : From fuel input(fuel cap/air vent) to output(carburetor).
■ Precautions before disassembly
Before performing disassembly operations, be
sure to drain all the fuel. Remove all dirt and dust
from each part. This is to prevent dirt from becom-
ing attached to the important locations.
Tool usage
Use the indicated tools correctly to avoid damag-
ing parts.
Only remove the parts that are necessary for
adjustment or repair, except when disassembling
for an overhaul.
During disassembly, try to memorize the location
and way each part is attached to avoid errors dur-
ing assembly. Label the parts if necessary.
Pay attention to small parts during disassembly
and check carefully for damage.
Be careful when handling gaskets and oil seals as
they can be damaged easily.
Be especially careful not to lose parts that have
been removed. Arrange the removed parts in a
pattern that approximates their actual position to
prevent loss or error.
Consider the assembly sequence when cleaning
the parts and wash the important parts first.
It is important to discriminate between the main
and sub-assembly steps.
■ Assembly precautions
Assembly sequence is reverse of disassembly.
Use new cleaning oil in the assembly and wash
each part while keeping the assembly sequence
in mind.
Verify the function of all disassembled parts or re
placement parts for assembly.
Adequately lubricate any revolving or rubbing
parts before assembly.
Always use new or complete gaskets. (As a
general rule, always use new parts for the
reassembly.)
Be sure to align all assembly marks.
Be careful not to tighten screws or bolts exces-
sively during assembly as they may be damaged.
Note:
1. Always use the correct tool for the particular
screw, bolt, nut or other part.
2. When there are a number of securing screws
or bolts for a part, tighten them equally in
an alternating sequence.
3. Tighten the nuts and bolts to the specified
torque.
4. Use Loctite#81666 to reform damaged
threads in plastic parts.
Note:
Do not use gasoline or oil to clean vibration
damping rubber.
11
STRATO CHARGED ENGINE
GZ25N
Wave
Washer
Clutch Shoe
Arrow marks on the
upper surface
6. SERVICE GUIDE
6-2 Removing of Clunch Shoe
Remove the housing and plug cap.
Remove the spark plug and fit the stopper (4810-
96220) into the plug hole.
Remove clutch bolts (14mm Hex.) .
Remove the rotor nut (12mm Hex.).
Remove the rotor using the puller assy (2890-
96100). Apply 8mm puller bolts.
6-3 Mounting of Clutch Shoe
6-4 Removing of Rotor
Apply grease into the holes on the clutch shoe
before mounting the clutch.
Grease : Molybdenum grease
Clutch bolt fixing torque:50 80kg.cm(43-69in.lbs）
Stopper
Clutch Bolt (14mm Hex
.)
Rotor Nut
Pulle
r
Puller bol
ts
Rotor
17mm Hex.
Clutch Shoe Grease
Caution:
Care for orientation of the wave washers and clutch
shoe.
12
STRATO CHARGED ENGINE
GZ25N
6. SERVICE GUIDE
6-6 Assembling of lgnition Coil
Insert the gauge (3350-96240) in between the rotor
magnet metal and the coil. Tighten screws while
pressing the coil against the rotor.
Gap specification 0.3 0.4mm(0.012 0.016in.)
Remove the recoil starter and the spark plug.
Insert the stopper (4810-96220) to the plug hole.
Engage the puller (4500-96100) to 2 holes on
the pulley and pull out the pulley.
Note:
Pulley screw is right turn screw.
6-5 Removing Recoil Pulley
Pulley
Pulle
r
Wrench
Ignition coil
Gauge
6-7 Installing of Spark Plug
The spark plug nut is 16mm hex. so that conven-
tional plug wrench (19mm) cannot be used.
Make sure to use the custom plug wrench.
Important:
Fixing the spark plug using other tools than the
custom plug wrench may apply over torque and end
up with damages of threads on the cylinder.
16mm
13
STRATO CHARGED ENGINE
GZ25N
6. SERVICE GUIDE
6-8 Laying of Switch Cable
Fit the lead wires with the clips on the side of the
coil. Confirm that they do not touch with the rotor.
6-9 Fitting of Plug Cap
Insert the guide of the plug cap into the engine
cover securely.
Caution:
Check that the plug cap is not deteriorated, stiffened,
nor has cracks.
Also check that there is no play after fitting the cap.
6-10 Removing Piston Pin
Remove snap rings from both sides of the piston
pin.
Engage the rod assy (1101-96220) to the piston
pin and gently tap with a plastic hammer to push
out the pin.
Caution:
Hard hammering may damage the big end of the
connecting rod.
Red
Black Clip
Coil
Engine Cover
Plug cap guide
Plastic Hammer
Rod Assy
Pisto
n
14
STRATO CHARGED ENGINE
GZ25N
6. SERVICE GUIDE
6-11 Installing of Piston
Make sure to point the arrow mark on the piston to
the exhaust side.
Caution:
Deformed circlip may come off during engine
operation and damage the engine.
6-12 Assembling of Piston Pin Circlip
Fit the circlip in the groove so as to face the end gap
below.
Exhaust side
Allow mark
Piston
Circlip
End Gap
6-13 Direction of Setting Cylinder Gasket
Set an arrow mark (punched out) on the cylinder
gasket toward the fan.
Caution:
An oppositely set gasket will touch with the insulator,
and makes a gap between the muffler. Therefore, the
cooling air to the cylinder is leaked toward the tank
and the cooling performance is reduced.
Cylinder Gasket
Arrow Ma
rk
15
STRATO CHARGED ENGINE
GZ25N
6. SERVICE GUIDE
6-15 Assembling of Cylinder Plate
A notch on the cylinder plate is to lay the high ten-
sion cable.
Set the cylinder plate with the notch at the muffler
side.
6-14 Positioning of Lead Air Intake Tube
The lead air intake tube has cast marking of either
“F”or“S”.
“S”is for the starter end, and“F”for the fan end.
Assembling position shall not be mixed up.
Caution:
Oppositely assembled tubes will cause a sealing failure.
Before assembling the tubes, check for deterioration or
cracks and change with new ones if necessary.
Marks
Lead air intake tube
6-16 Setting of Insulator Gasket
Set the insulator gasket under the engine cover with
care for not turning it up by the engine cover.
Insulator Gasket
Muffler side
Notch
Cylinder Plate
16
STRATO CHARGED ENGINE
GZ25N
6. SERVICE GUIDE
6-17 Mounting of Reed Valve
Check that there is no foreign matter inside the valve
case.
Important:
Check the gap between the valve case and the reed
valve.
Replace with new valve if the gap is larger than
0.2mm (0.008in.), or the valve is distorted.
Screw lock agent shall be applied to the reed valve
and the stopper fixing screw.
The reed valve case has a marking either“S”or
“F”.
“S”is for the starter side, and“F”for the fan side.
Assembling position shall not be mixed up.
Max. 0.2mm
Reed Valv
e
6-18 Removal of Clutch Drum
Remove the snap ring on the clutch drum end
using a snap ring pliers (5500-96110).
1) Removing Snap Ring
Snap Ring
Pliers
Snap Ring
Clutch Drum
Housing Assy
17
STRATO CHARGED ENGINE
GZ25N
6. SERVICE GUIDE
Caution:
Make sure to replace the snap ring if it is deformed.
Assembling shall be done by an reverse order to
the disassembling.
・ Assemble the clutch drum into the clutch housing
and set the snap ring using a snap ring guide
(5500-96130) and the snap ring push guide (5500-
96140).
・After the assembly, apply molybdenum grease
on the clutch drum spline.
6-19 Assembling Cluch Drum
1) Assembling Snap Ring
Snap Ring
Push Guide
Clutch Drum
Snap Ring
Guide
Snap Ring
Tap the stopper by hand and engage the snap
ring into the drum groove.
Molybdenum Grease
2) Applying grease
Hold the drum remover (5500-96120) on the clutch
drum, and gently hammer to pull out the clutch
drum.
2) Removing Clutch Drum
Hammer
Drum Remover
Clutch Drum
18
STRATO CHARGED ENGINE
GZ25N
7-2 Function and Operation of Throttle Valve
7-1 Construction
The Strato-charged Engine is applied with a custom designed carburetor employing diaphragm rotary
valves and 2 venturies, one for the lead air and the other for the air-fuel mixture.
The throttle valve has 2 ports. Upper port is for
the lead air and lower port for the air-fuel mixture.
As shown above, the rotary valves are coaxially
arranged while their air passage bores and valve
outside diameters differ each other. As the venturi
bore sizes also differ each other, air intake timing
can be changed by rotation of the rotary valves.
Intake timing for the air-fuel mixture and the
lead air are as illustrated below:
Idling
Lead air : Close
Mixture : Start to open
Mid speed
Lead air : Start to open
Mixture : Half open
High speed
Lead air : Full open
Mixture : Full open
Air Cleaner
Carburetor
Throttle Valve
Air-fuel Mixture
Lead Air
Insulator
Lead Air Intake Tube
To Reed Valve
: Lead Air Port
: Air-fuel mixture Port
18
A
B
A
B
8
9
8
9
13.0
18.1
Lead Air block
Air-fuel Mixture
block
unit: mm
Venturi bore
Rotary Valve
7. CARBURETOR
STRATO CHARGED ENGINE
GZ25N
19
STRATO CHARGED ENGINE
GZ25N
7. CARBURETOR
7-3 Specifications
Item Unit Specifications
Product Name
Engine Type GZ25N
Carburetor
Type Name WYA-1B
Part Number 4810-81001
Carburetor Specification
Main Jet #38.5
Metering Lever Height mm (in.) 1.5 ±0.16 (0.059 ±0.006)
Venturi Bore mm (in.) MIX 9.0 (0.354) AIR 8.0 (0.315)
Choke Bore mm (in.) ø13.2 (ø0.5210)
Valve Opening Pressure kg/cm2 (psi) 1.0 2.0 (14.2 28.4)
Valve Closing Pressure kg/cm2 (psi) 0.4 1.4 (5.69 19.91)
Speed
Idling rpm 2800 3200
Clutch engaging rpm 3800 4200
Stall rpm 5650 6150
Operating Speed rpm 6000 10000
No Load Max Speed rpm 10000
20
STRATO CHARGED ENGINE
GZ25N
7. CARBURETOR
7-4 Composition and Inspection a) Adjusting Idle Speed
The idle speed is set for 3000rpm at the factory. If it
is necessary to adjust the idle speed, use the adjust-
ment screw on the top side of carburetor
(Main Jet No. : #38.5)
b) Judgement of the main check valve
As illustrated, hold a plastic pipe on the check valve
and blow and suck air by your mouth. If the air is
stopped by blowing, and open by sucking, the valve
has no failure.
In case of failure, soak the valve into gasoline for
about 10 minutes and repeat blowing and sucking
several times. If this is not successful, exchange
with new one.
(Make sure to check the valve in case fuel is not
supplied though the priming pump is operated)
Screw
Bracket
Washer
Throttle Valve
Carburetor Body
O-ring
Main Jet(♯38.5)
Pump Diaphragm
Screen
Body
Valve
Pin
Screw
Diaphragm
Purge body
Priming Pump
Pump Cove
Screw
Gasket
Lever
Spring
Gasket
O-ring
Clip
Swivel
Adjust Nut
Adjust Screw
Adjustment Screw
Adjustment
Screw
Plastic Pipe
Main Check Valve
21
STRATO CHARGED ENGINE
GZ25N
8. TROUBLE SHOOTING
8-1 Engine does not start
Description Cause Countermeasure
No spark in the spark plug
Spark Plug 1.Wet spark plug electrodes Make them dry
2.Carbon deposited on the electrodes Cleaning
3.Insulation failure by insulator damage Exchange
4.Inproper spark gap
Adjust to 0.6-0.7mm (0.023-0.028in.)
5.Burn out of electrodes Exchange
Magneto 1.Ignition coil inside failure Exchange
2.Damaged cable sheath or disconnected cable
Exchange or repair
Switch 1.Switch is OFF ON the switch
2. Switch failure Exchange
3. Primary wiring earthed Repair
Sparks appear in the spark plug
Compression & 1.Over sucking of fuel Drain excess fuel
2.Too rich fuel Adjust carburetor
3.Overflow Carburetor adjust or exchange
4. Clogging of air cleaner Wash with mixed gasoline
5.Faulty fuel Change with proper fuel
Fueling normal but
1.Worn out cylinder, piston, or piston ring
Exchange
2.
Gas leakage from cylinder and crank case gasket
Apply liquid gasket and reassemble.
No fuel supply 1. Choked breather air hole Cleaning
2.Clogged carburetor Cleaning
3.Clogged fuel filter Exchange fuel filter
fueling is normal
poor compression
8-2 Stalled during Operation
Description Cause Countermeasure
Suddenly stopped 1.Switch is OFF ON the switch
2.Plug cap disconnected Properly fit as original
3.Short circuit of spark plug electrodes by carbon
Remove carbon
4. Switch cable or high tension cable Exchange
sheath worn out
5. Ignition coil inside failure Exchange
6. Engine seizure Overhaul
Gradual speed reduction 1.Lack of fuel Supply fuel
2.Clogging inside carburetor Cleaning
3.Water mixed to fuel Drain and apply new fuel
and stalled
22
STRATO CHARGED ENGINE
GZ25N
8. TROUBLE SHOOTING
8-3 Engine cannot be stopped
8-4 Lack of output power or unstable revolution
Description Cause Countermeasure
Overheating 1.Lean fuel Adjust carburetor
2.Cylinder fin clogged with dusts Cleaning
3.Inproper fuel Change with proper fuel
4.Carbon deposited inside of combustion Cleaning
chamber
5.Spark plug electrode red hot Clean thoroughly and adjust
spark gap
[ 0.6-0.7mm (0.023-0.028in.) ]
Switch 1.Faulty switch Exchange
2.Cable failure Repair
Description Cause Countermeasure
Compression is normal
1. Air penetration from fuel pipe joints, etc
Secure connection
2. Air penetration from intake tube joint Change gasket or tightening
or carburetor joint screws
3 Water in fuel Change with good fuel
4. Piston start to seizure
Filing of seized surface with fine files
5. Muffler choked with carbon Cleaning
6. Crack on lead air intake pipe Exchange
7.
Reed valve clogged with dusts or valve
Cleaning or exchange
tip opening is larger than specification components
[ 0.2mm (0.008in.) ]
8. Reed valve stuck Cleaning or exchange
Overheating 1. Fuel too lean Adjust carburetor
2. Clogging of cylinder fin with dust Cleaning
3. Poor fuel quality Exchange with proper fuel
4. Carbon deposited in the combustion Cleaning
chamber
5. Spark plug electrode red hot Thoroughly clean, adjust spark
gap
[ 0.6-0.7mm (0.023-0.028in.) ]
Others 1. Dirty air cleaner Wash with mixed gasoline
2. Over loading Reduce load
and no misfire
Note : Hatched columns above are potential failures unique to the stratified scavenging engine.
23
STRATO CHARGED ENGINE
GZ25N
R
KOMATSU ZENOAH AMERICA INC.
4344 Shackleford Road, Suite 500
Norcross, Georgia, 30093
