Eton VIPER 50 ST - SERVICE User manual

SERVICEMANUAL

CONTENTS
1. INFORMATION
2. MAINTENANCE
3. ENGINE REMOVAL AND INSTALLATION
4. ENGINE FUEL SYSTEM
5. ENGINE LUBRICATION AND COOLING SYSTEM
6. ENGINE COMBUSTION SYSTEM
7. TRANSMISSION SYSTEM
8. STEERING SYSTEM
9. FRONT WHEEL SYSTEM
10. REAR WHEEL SYSTEM
11. FENDERS AND EXHAUST PIPE
12. ELECTRICAL SYSTEM
13. TROUBLE SHOOTING

1. INFORMATION
1.1 SAFTY
1.2 NOTES
1.3 SPECIFICATION
1.4 SERIAL NUMBER
1.5 TORQUE VALUE
1.1 SAFETY
GASOLINE
Gasoline is extremely flammable and is explosive under certain condition.
Do not smoke or allow sparks or flames in your work area.
● CARBON MONOXIDE
Never run the engine in a closed area. The exhaust contains poisonous carbon
monoxide gas that may cause loss of consciousness and lead to death.
● BATTERY ELECTROLYTE
The battery electrolyte contains sulfuric acid. Protect your eyes, skin and
clothing. If you contact it, flush thoroughly with water and call a doctor if electrolyte
gets in your eyes.
●HOT PARTS
Engine and exhaust pipe become very hot and remain hot for one hour after the
engine is run. Wear insulated gloves before handling these parts.
●USED ENGINE/GEAR OIL
Used engine oil and gear oil may cause skin disease if repeatedly contact with
the skin for long periods.
Keep out of reach of children.
1.2 NOTES
All information, illustrations, directions and specifications included in this publication are base on the latest
product information available at the time of approval for printing.
JI-EE Dynamic Technology Industry Co., Ltd. reserves the right to make changes at any time without notice
and without incurring any obligation whatever.
No part of this publication may be reproduced without written permission.
2

1.3 SPECIFICATION ENGINE (for
V
iper
ST
&Yukon
ST in this service manual)
COLORING
Specifications subject to change without notice.
3
Viper
ST EXL-50 Yukon ST EXL-50
SUSPENSION
Front Single A-arm / Adjustable Shocks
Rear Swing Arm / Adjustable Shock
BRAKES
Front Dual Mechanical drum
Rear Hydraulic Disc
TIRES
Front 20/6-10
Rear 20/10-9
PRESSURE 【psi (0.23 kgf/cm
2
)】
Front 12(0.8) 12(0.8)
Rear 12(0.8) 12(0.8)
V
i
p
er
ST
EXL-50 Yukon
S
T
EXL-50
CHASSIS
Overall Length 1670 mm 1750 mm
Overall Width 940 mm 1010 mm
Overall Height 1040 mm 1065 mm
Seat Height 760 mm 760 mm
Wheel base 1110 mm 1115 mm
Ground Clearance 120 mm 120 mm
Dry Weight 152 kg 152 kg
Fuel Tank Capacity 4.5 Liters 4.5 Liters
Type Two cycle air cooled
Displacement 49.3 c.c.
Bore and Stroke 40.0
X
39.2mm
Compressionratio 6.8:1
Maximum Torque (Nm/rpm)
4.5 Nm
/
6000
r
p
m
Carburetor Piston type
Ignition Capacitor Discharge
Starting Electric and kick starter
Lubrication Forced pressure and wet sump
Transmission Automatic (C.V.T. V-belt) Fr Neut .Rev
Maximum Power (ps/rpm) 3.8 ps/6000rpm

1.4 SERIAL NUMBER
(For ViperST EXL-50 / YukonST EXL-50 in this service manual)
The frame serial number is stamped on the front of the frame.
The engine serial number is stamped on the left side of the crankcase.
Frame serial number
Engine serial number
4

.5 TORQUE VALUES
(For EXL 50 in this service manual)
STANDARD
●5 mm bolt and nut 5 N.m (3.5 lbf.ft)
●6 mm bolt and nut 10 N.m (7.2 lbf.ft)
●8 mm bolt and nut 22 N.m (16 lbf.ft)
●10 mm bolt and nut 35 N.m (25 lbf.ft)
●12 mm bolt and nut 55 N.m (40 lbf.ft)
ENGINE
●Cylinder head nut 28 N.m (20.7 lbf.ft)
●Spark plug 12 N.m (8.9 lbf.ft)
●Cylinder head bolt 20 N.m (14.8 lbf.ft)
●Alternator bolt 8 N.m (5.9 lbf.ft)
FRAME
●Handlebar upper holder bolt 24 N.m (17.7 lbf.ft)
●Throttle housing cover screw 4 N.m (2.9 lbf.ft)
●Steering shaft nut 50 N.m (36.9 lbf.ft)
●Steering shaft holder bolt 33 N.m (24 lbf.ft)
●Wheel rim bolt 18 N.m (13.3 lbf.ft)
●Tie rod lock nut 35 N.m (25.8 lbf.ft)
●King pin nut 40 N.m (29 lbf.ft)
●Handlebar lower holder nut 40 N.m (29.5 lbf.ft)
●Front wheel bolt 24 N.m (17.7 lbf.ft)
●Front axle castle nut 40-60 N.m (30-45 lbf.ft)
●Front brake arm nut 4 N.m (3.0 lbf.ft)
●Rear brake arm nut 7 N.m (5.2 lbf.ft)
●Rear axle castle nut 40-60 N.m (30-45 lbf.ft)
●Rear wheel bolt 24 N.m (17.7 lbf.ft)
●Exhaust muffler mounting bolt 30 N.m (22.1 lbf.ft)
●Engine hanger bolt 30 N.m ( 22 lbf.ft)
●Rear axle holder bolt 90 N.m (65 lbf.ft)
●Swing arm pivot nut 90 N.m (65 lbf.ft)
●Rear shock absorber mounting nut 45 N.m (33 lbf.ft)
5

2. MAINTENANCE
2.1 MAINTENANCE DATA 2.8 IDLE SPEED
2.2 MAINTENANCE SCHEDULE 2.9 DRIVE CHAIN
2.3 FUEL TUBE 2.10 BRAKE SYSTEM
2.4 THROTTLE OPERATION 2.11 WHEELS AND TIRES
2.5 THROTTLE CABLE ADJUSTMENT 2.12 STEERING SYSTEM
2.6 AIR CLEANER 2.13 TOE-IN
2.7 SPARK PLUG 2.14 GEAR OIL
2.1 MAINTENANCE DATA
SPECIFICATION
SPARK PLUG:
SPARK PLUG GAP: 0.6-0.7 mm
RECOMMENDED SPARK PLUGS: NGK BPR7HS
THROTTLE LEVER FREE PLAY: 5-10 mm
IDLE SPEED: 1800±100 rpm
BRAKE LEVER FREE PLAY:
15-25 mm
DRIVE CHAIN SLACK
10-25 mm
FRONT/REAR TIRE PRESSURE MIN 2 psi (12.5kpa)
TOE-IN 5±10 mm
TORQUE VALUES
SPARK PLUG 25-30 N.m
TIE-ROD LOCK NUT 35-43 N.m
ENGINE OIL JASO FC Grade or same degree oil
GEAR LUBRICATION OIL SAE 90
2.2 MAINTENANCE SCHEDULE
The maintenance internals in the follow table is based upon average riding, conditions. Riding in unusually
dusty areas, require more frequent servicing. (For ATV all serial in this service manual)
INITIAL SERVICE
(
First week
)
REGULAR SERVICE
(
E
v
er
y
30 operatin
g
da
y
s
)
EVERY YEAR
FUEL LINE
THROTTLE OPERATION
AIR CLEANER
SPARK PLUG
CARBURETOR IDLE SPEED
DRIVE CHAIN
BRAKE SHOE WEAR
BRAKE SYSTEM
NUT, BOLT, FASTENER
WHEEL
STEERING SYSTEM
SUSPENSION SYSTEM
C.V.T. AIR FILTER
GEAR OIL
REVERSE GEAR OIL-RXL90R
I
I
I, L
I
I
I
I
C
I
I
I, L
I
I
I
C
I
I
I
I
R
R
Note – I: Inspect and Clean, Adjust, Lubricate or Replace, if necessary
C: Clean L: Lubricate R: Replace

2.3 FUEL TUBE
Inspect the fuel lines for deterioration, damage or
leakage and replace if necessary.
2.4 THROTTLE OPERATION
Inspect for smooth throttle lever full opening and
automatic full closing in all steering positions.
Inspect if there is no deterioration, damage or kinking
in the throttle cable, replace it if necessary.
Check the throttle lever,
free play is 5-10 mm at the tip
of the throttle lever.
Disconnect the throttle cable at the upper end.
Lubricate the cable with commercially lubricant to
prevent premature wear.
2.5 THROTTLE CABLE ADJUSTMENT
Slide the rubber cap of the adjuster off the throttle
Housing, loosen the lock nut and adjust the free play
of the throttle lever by turning the adjuster on the throttle
housing. Inspect the free play of the throttle lever.

2.6 AIR CLEANER
Unscrew the air cleaner cover screws.
Pull out the air filter element from the air cleaner case.
Wash the element in non-flammable solvent, squeeze
out the solvent thoroughly.
Let it dry.
Soak the filter element in gear oil and then squeeze
out the excess oil.
Install the element into air cleaner carefully.
2.7 SPARK PLUG
This spark plug located at the front of the engine.
Disconnect the spark plug cap and unscrew the spark plug.
Check the spark plug electrodes for wearness.
Change a new spark plug if the electrodes and insulator tip
appear unusually fouled or burned.
Discard the spark plug if there is apparent wear or if the
insulator is cracked or chipped.
The spark plug gap shall keep in 0.6-0.7mm.
With the sealing washer attached, thread the spark plug in
by hand to prevent cross threading.
Tighten the spark plug with 25-30 N.m
2.8 IDLE SPEED
Connect an engine speed meter.
Warm up the engine, 10 minutes are enough.
Turn the idle-speed adjust screw on the carburetor
to obtain the idle speed. “Turn in” (clockwise) will get higher
speed. “Turn out” (counter clockwise) will get lower speed.
IDLE SPEED: 1800±100 rpm
2.9 DRIVE CHAIN
Inspect the chain slack. The standard is 10-25mm.

Adjust the chain slack.
Loose the lock bolts (4 pcs) then adjust the drive chain
slack by turn the adjusting nut.
Tighten the four lock bolts.
When the drive chain becomes very dirty, it should be
removed, cleaned and lubricated by specify lubricator.
Using commercial chain lubricant to lubricate the drive
chain.
Clean the drive chain with kerosene and wipe it dry.
Inspect the drive chain for possible wear or damage.
Replace the chain, if it is worn excessively or damaged.
Inspect the sprocket teeth, if it is excessive wear
or damage, replace it.
Inspect the chain-tensioned roller.
Replace it, if necessary.
2.10 BRAKE SYSTEM
Inspect the front brake lever and cable for excessive
play or other damage.
Replace or repair if necessary.
Measure the free play of the brake lever at the end of the
brake lever.
The standard of free play is 15-25 mm.

Inspect the rear brake lever and cable for excessive
play
or other damage.
Replace or repair if necessary.
Measure the free play of the rear brake lever at the end of
the
lever. Th e standard is 15-25 mm.
BRAKE SHOE WEAR
FRONT
BRAKE
Release the front wheel and inspect the brake lining
thickness.
Service Limit: 2 . 0mm(0.08 inch)
If either lining is worn beyond the service limit, replace
Both brakes shoes.
2.11 WHEELS AND TIRES
Inspect the tire surfaces for cuts, nails or other sharp objects.
Check
the tire surfaces at cold tire condition.
The standard of tire pressure is 1 . 2±0.3 ps i.
(0.8 k g f/cm
2
)
2.12 STEERING SYSTEM
Check the free play of the steering shaft with the front wheels,
turned
straight ahead.
When there is excessive play, inspect the tie-rod, kingpin
bushing
and ball joint.

STEERING SHAFT HOLDER BUSHING
Remove the front fender first.
Remove the steering shaft holder and check the steering
shaft bushing for wears or damage.
If the bushing is worn or damaged, change a new
one.
Grease the steering shaft bushing and install the parts in the
reverse order of removal.
Torque: steering shaft holder bolt: 33 N.m (24 lbf.ft)
2.13 TOE-IN
Let the vehicle on level ground and the front wheels facing
straight ahead.
Mark the centers of the tires to indicate the axle center
height.
Measure the distance between the marks.
Carefully move the vehicle back, let the wheels have
turned 180 °, so the marks on the tires are aligned
with the axle center height.
Measure the distance between the marks.
Calculate the difference in the front and rear
measurements.
Toe-in: 5±10mm
If the toe-in is out of standard, adjust it by changing
the length of the tie-rods equally by turning the tie-rod
while holding the ball joint.
Tighten the lock nuts.
Torque: 35-43 N.m

2.14 GEAR OIL
Gear oil needs to be changed every year.
There is a gear oil release bolt at the rear of engine.
Unscrew this release bolt and can let the dirty oil flow out.
The re-add oil hole is on the engine case beside gearbox.

3. ENGINE REMOVAL AND INSTALLATION
3.1 SERVICE INFORMATION 3.3 ENGINE INSTALLATION
3.2 ENGINE REMOVAL
3.1 ENGINE SHALL BE REMOVED IN THE CONDITIONS OF NECESSARY REPAIRMENT OR
ADJUSTMENT TO THE TRANSMISSION AND COMBUSTION SYSTEM ONLY
3.2 ENGINE REMOVAL
Remove the seat and rear fender. (Chapter 11) Remove the
spark plug cap from the spark plug. Remove the exhaust
pipe.
Disconnect the carburetor cable by unscrew two screws on
top of the carburetor.
Take off oil pump cable from the oil pump control plate. Oil
pump is under the right side of engine.
Disconnect the wire connectors. There are three
connectors for carburetor auto-choke, starter motor
and generator respectively.
Remove the drive chain cover. This is under the chain.
Remove the drive chain retaining clip and master link,
and remove the drive chain.
Remove the three engine hanger nuts and bolts.
Remove the engine from the right side of frame.

3.3 ENGINE INSTALLATION
Engine installation is essentially the reverse order of removal.
The torque of engine hanger bolt is 24-30 Nm
Route the wires and cable in reverse order properly.

★UNPROPER ADJUSTMENT TO THE
POORLY I
DLE SPEED SCREW
★I
GNITION MALFUNCTION
★F
UEL / AIR MIXTURE RATIO NO GOOD
★A
IR CLEANER DIRTY
★I
NSULATOR LEAKS
★F
UEL TANK CAP BREATHING HOLE
CLOGGED
L EAN MIXTURE ★ FUEL JET OF CARBURETOR CLOGGED
★F
UEL TANK CAP BREATHING HOLE
CLOGGED
★F
UEL FILTER CLOGGED
★F
UEL FLOWS IN THE TUBE
UNSMOOTHLY
★F
LOAT LEVEL IN CARBURETOR TOO
LOW
R ICH MIXTURE ★F LOAT NEEDLE VALVE IN
CARBURETOR FAULTY
★F
LOAT LEVEL TOO HIGH
★A
IR DUCT IN CARBURETOR IS
CLOGGED
★A
IR CLEANER DIRTY

4.1FUEL TANK
REMOVAL
Remove the seat and rear fender.
Disconnect the fuel line from the carburetor.
Remove the fuel tank cap and front fender.
Unscrew the fuel tank fixed bolts.
Note: Keep gasoline away from flames or sparks.
Wipe up spilled gasoline at once.
4.2CARBURETOR
REMOVAL
Remove the air cleaner.
Disconnect the fuel line and auto-choke electric wire.
Unscrew the intake pipe mounting bolts at the
carburetor then removes the carburetor.
Note: Turn fuel cup on (off) position
Remove the carburetor cap.
Remove the throttle cable from the throttle valve while
depressing the throttle valve spring.
Remove the needle clip retainer, the jet needle and
needle clip. Inspect the throttle valve and
jet needle surface for wearness, scratches or dirt.
4. ENGINE FUEL SYSTEM
4.1 FUEL TANK 4.2 CARBURETOR

DISASSEMB
L
Y
Unscrew the float chamber screws and remove
the carburetor chamber.
Disassembly the float and float needle
valve.
Inspect the seat of the float needle valve for
wear or damage.
Disassembly the slow jet, main jet, throttle adjusting
screw and air flow adjusts screw.
Inspect all the jets and screws for wear or damage. Clea
n
the passages and jets with compressed air.
carbureto
r
chambe
r
slow
j
et
main
j
et
throttle adjusting sc
r
ew
ai
r
flow ad
j
usts sc
r
ew

ASSEMBLY
Clean all parts in solvent and blow it dry with compressed air.
Assembly is essentially the reverse order of disassembly.
THROTTLE VALVE ASSEMBLY
Install the needle clip on the jet needle.
Install the jet needle into the throttle valve.
Assembly the throttle cable, spring and the throttle valve.
Align the throttle valve groove with the idle speed adjust
screw and install the carburetor cap to the carburetor.

5. ENGINE LUBRICATION AND COOLING SYSTEM
5.1 ENGINE LUBRICATION SYSTEM 5.4 COOLING SYSTEM
5.2 CAUTION
5.3 OIL PUMP
5.5 TROUBLESHOOTING
5.1 ENGINE LUBRICATION SYSTEM
The engine drives the pump gears of oil pump
crankshaft. Pump gears rotate the plunger shaft in oil
pump. This shaft sent the lubricating oil into the crankcase
to mix with the mixture of air-fuel flow evenly.
The oil drops and foam cover the cylinder inner wall,
piston surface and piston rings.
5.2 CAUTION
Having enough oil supply to engine is very important.
If the oil quantity is not enough, this engine will be serious scratched, and then this engine will stop, even
cannot work again.
When this engine is serious scratched, you need to change the piston, piston rings and cylinder together.
Also you need to check the combustion system and lubrication system carefully.
5.3 OIL PUMP
The quantity of oil that deliver out from oil pump increased by the engine speed and the carburetor throttle
open width. Oil pump is under the right side of the engine and connected by a control cable of throttle.
5.4 COOLING SYSTEM
The engine-cooling fan sucks the air.
The cooling fan is on the right side of engine.
The air is forced to flow through cylinder fin and
cylinder head. So, the cylinder and piston will not
over heat.