Yamaha LB50IIAC User manual

YAMAHA
4RP-28197-20

EBOOOOOO
LB50 II AC/LBBO II AC
SERVICE MANUAL
©1997 by Yamaha Motor Co., Ltd.
First
edition, March 1997
All rights reserved. Any reproduction or
unauthorized use without the written
permission of Yamaha Motor Co., Ltd.
is expressly
prohibited.

INDEX
GENERAL INFORMATION
PERIODIC INSPECTIONS
AND ADJUSTMENTS
, ENGINE OVERHAUL
CARBURETION
CHASSIS
ELECTRICAL
APPENDICES

CHAPTER 1. GENERAL INFORMATION
FEATURES .......................................................................................................................1
MACHINE IDENTIFICATION............................................................................................5
EXTERNAL
VIEW .............................................................................................................6
SPECIFICATIONS.............................................................................................................8
GENERAL SPECIFICATIONS...................................................................................8
MAINTENANCE SPECIFICATIONS....................................................................... 11
GENERAL TORQUE SPECIFICATIONS......................................................................... 19
CABLE ROUTING...........................................................................................................20
SPECIAL TOOLS ............................................................................................................
29

CHAPTER 1.
GENERAL INFORMATION
FEATURES
Automatic mechanism
1. Using a pair of shoe-type centrifugal clutches. the drive ratio is changed automatically.
®
@-------'
®
©-----~
1
1st drive gear 9. Spring 16.
low range
2. Clutch housing 10:
2nd drive gear 17. High range
3.
1st clutch 11.
Shift rod 18. Drive axle
4.
2nd clutch 12.
Main axle 19. 1st driven gear
5.
One-way clutch
13. One-way clutch
20
Spring
6 Crankshaft
14
2nd driven gear 21. Kick gear
7.
Shift lever 15. Sprocket
22 Kick crank
8. Kick pinion
- 1-

2. The use of an automatic 2-speed centrifugal clutch relieves the rider from the cumbersome
operation of the shift lever. That is, ease of operation and additional safety are ensured for
the rider. When starting out, gears are automatically shifted into first, and then into second
according
to engine load. This will result in a longer life of the engine.
Automatic transmission mechanism
The automatic transmission mechanism consists of two shoe-type centrifugal clutches.
1st gear clutch: -, FGr starting out and for 1st gear operation.
2nd gear clutch: -, For automatic change to 2nd gear.
1. Each clutch has three clutch shoes
operated
by centrifugal force. These
shoes are
well balanced to minimize the
vibration for smooth operation.
This clutch is provided with linings of
high wear-resistance. and thus excellent
clutching power is guaranteed. The
heat generated by friction between
shoes and lining is quickly dissipated
through the gear oil to the clutch hous-
ing,
with which the clutch shoes are in
contact.
2. The 2nd gear side is provided with an
overrunning clutch.
3.
An overrunning clutch for starting is
built in the hub of driven gear 1. Longer
life is ensured
by simple construction.
1st clutch
2nd clutch
1st driven gear
-2-

Theory of operation
1. Idling
At idling, the 1st gear side clutch driven
by the crankshaft is
kept uncoupled by
spring force, because of the centrifugal
force exerted on
the weights.
2. Starting out with 1st gear
As the throttle grip is twisted open, the
engine speed increases, and the spring
force is
overcome by the centrifugal
force, and
the clutch shoes are forced
against
the clutch housing, causing fric-
tion. As
the friction increases, the tur-
ning force of the engine is transmitted
to the main axle through 1st drive and
driven gears.
3. Reduction and
2nd gear
As the throttle grip is further opened,
the
2nd side clutch begins to operate.
That is,
the clutch shoes are forced
against
the clutch housing by the
weights, and thus the engine power is
transmitted through 2nd drive and
driven gears
to the main axle.
At this stage, the 1st gear side clutch is
released because
it is an overrunning
clutch.
-3-
t. Clutch housing
2
1st dutch
3. 2nd clutch
4. 1st drive gear
5. 1st driven gear
1. Subtransmission
2. Rear wheel
G
CD
@
(j)
®
6. 2nd drive gear
7.
2nd driven gear
8. Main axle
9. One-way dutch
c-
1
_---1-1-----=-.l-l- c
CD
c1
1. Subtransmission
2. Rear wheel

4. Sub-transmission mechanism
In order to increase the engine torque
required for climbing a hill with ease,
this motorbike is equipped with a
subtransmission.
5. Operation of the lever
D-range:
Driving on level roads
N-range:
Neutral (Engine
warming up)
L-range:
Climbing
up a steep slope
NOTE:-----------
1. The shift lever must be operated at
idling.
2. In
order to change to the "L" range,
first push
down the stopper lever
and
then set the shift lever to "L".
Kick starter mechanism
1. Both kick idle gear and kick pinion are
helically meshed.
When kicked, thrust
is exerted on the pinion, thus causing it
to move off the drive axle.
2.
When the kick crank returns to its home
position after the engine is started, the
kick
pinion is forced back by the return
spring.
1 Dock
2 Main axle
3 Driven gear
4. Drive axle
1 One way clutch
2 Main axle
3 Drive axle
4
Ratchet wheel
5 Kick crank
-4-
5 Drive range
6 Low range
7 Sprocket
8. Shift rod
@ ® ©
~I/
6 Kick gear
7 Kick idle gear
8 Dock
9 Driven gear

MACHINE IDENTIFICATION
The frame serial number is located on the
right-hand side of the headstock assembly.
The
first three digits identify the model. This
is followed by a dash. The remaining digits
identify the production number of the unit.
The engine serial number is located on a rais-
ed boss
on the upper front, left-hand side of
the engine. Engine identification follows the
same code as frame identification.
Normally, both serial numbers are identical;
however, on occasion they may be two or
three numbers off.
Starting Serial Number
439-1000101 (LB50 II AC)
34H-010101 (LB80 II AC)
Frame serial number
Engine serial number
-5-

EXTERNAL VIEW
LB50 II AC
1------ww oiL--~-i
-6-
E
E
0
E
~
E
"\
~
~
o_

LB80IIAC
WW QLL
-7-
E
E
"'
"'
E "'
E
0
q

SPECIFICATIONS
GENERAL SPECIFICATIONS
Model LB50 II
AC
Model code: 4F4
Engine
starting number:
439-1000101
Frame
starting number:
439-1000101
Dimensions:
Overall length 1,570
mm
Overall width
665 mm
Overall height
925mm
Seat height
710 mm
Wheelbase 1,075
mm
Minimum ground clearance 135
mm
Minimum turning radius 1,500
mm
Basic weight:
With oil and full fuel tank 80 kg
Engine:
Engine
type
Air cooled 2-stroke
Induction system
Torque induction
Cylinder arrangement
Single cylinder, for-
ward inclined
Displacement
49 cm
3
Bore x stroke 40.0 x 39.7
mm
Compression ratio 6.6:1
Starting system
Kick starter
Lubrication system: Separate lubrication
(Yamaha autolube)
Oil type
or grade:
Engine
oil
Air cooled 2-stroke
engine oil
Transmission
oil
SAE 10W30 type SE
motor oil
Oil capacity:
Oil
tank (engine oil) 1.4 L
Transmission
oil
Periodic oil change 0.65 L
Total
amount
0.7 L
Air filter:
Wet type element
Fuel:
Type Regular unlead gaso-
line
Fuel
tank capacity
3.5 L
Fuel reserve
amount
0.5 L
Carburetor:
Type I
quantity
VM14SC/1
Manufacturer
MIKUNI
-8-
LB80 II AC
4RP
34H-010101
34H-010101
1,565
mm
f-
f-
f-
1,050 mm
f-
f-
76 kg
f-
f-
f-
72 cm
3
47.0 x 42.0 mrn
5.8:1
f-
f-
f-
f-
f-
f-
f-
f-
f-
f-
0.3 L
VM16/1
f-

Model LB50 II AC LB80 II AC
Spark plug:
Type B6HS
f-
Manufacturer
NGK f-
Spark plug gap
0.5 -0.6 mm
f-
Clutch type: Wet, centrifugal auto-
f-
matic
Transmission:
Secondary reduction system Chain
drive f-
Secondary reduction ratio 31/14 (2.214) 30/15 (2.000)
Transmission
type Constant mesh 2- f-
speed automatic
Operation
Centrifugal automatic f-
type
Gear ratio 1st 69/18 (3.833)
f-
2nd 59/28 (2.107) f-
Sub-transmission ratio low 39/12 (3.250) f-
Sub-transmission ratio high 35/16 (2.188) 29/15 (1.933)
Chassis:
Frame type Steel tube
underbone f-
Caster angle 26'
f-
Trail 45mm
f-
Tire:
Type
With tube
f-
Size front
4.00-8-4PR f-
rear 4.00-8-4PR
f-
Manufacturer front INOUE
f-
rear INOUE
f-
Tire pressure (cold tire):
Loading
condition A * 0 - 70 kg
0 - 74 kg
front
100 kPa (1.00 kg/cm', f-
1.00 bar)
rear 125
kPa (1.25 kg/cm', f-
1.25 bar)
Loading
condition B * 70
-140 kg 74-144kg
front
100 kPa (1.00 kg/cm', f-
1.00 bar)
rear 200
kPa (2.00 kg/cm', 150 kPa (150 kg/cm',
2.00 bar) 1.50 bar)
Brake:
Front brake type Drum brake f-
operation
Right hand operation f-
Rear brake type
Drum brake f-
operation
Left hand operation f-
*Load 1s the total weight of cargo, rider, passenger and accessories.
-9-

Model LB50 II
AC LB80 II AC
Suspension:
Front suspension Telescopic
fork
,----
Rear suspension
Swingarm
,----
Shock absorber:
Front shock absorber Coil spring I Oil
,----
damper
Rear shock absorber Coil spring I Oil
,----
damper
Wheel travel:
Front wheel travel
75 mm
,----
Rear wheel travel
84mm
80 mm
Electrical:
Ignition system C.D.I.
,----
Generator system Flywheel
magneto
,----
Battery type
6N4-2A-2
,----
Battery capacity 6 V 4 AH
,----
Headlight type: Bulb
type
,----
Bulb wattage x quantity:
,----
Headlight 6 V
25 W /25 W
,----
Tail I brake light
6 V 5.3 WI 17 w
,----
Flasher light
6V10Wx4
,----
Meter light
6V3Wx1
,----
High beam indicator light
6V3Wx1
,----
Oil level indicator light 6V3Wx1
,----
-10 -

MAINTENANCE SPECIFICATIONS
ENGINE
Cylinder head:
Warp
limit
Cylinder:
Bore size
Taper
limit
Model
Out of round limit
Piston:
,-*
Piston to cylinder clearance
<Limit>
Piston size "D"
Measuring point "H"
Oversize
Oversize
Piston
off-set
Piston off-set direction
Piston pin bore inside diameter
Piston pin outside diameter
Piston rings:
Top ring:
1st
2nd
CJ]s
Type
Dimensions (Bx T)
End gap (installed)
I T I
Side clearance (installed)
LB50 II
AC
0.03 mm
40.00 -40.02 mm
0.05 mm
0.01 mm
0.025 -0.030 mm
<0.1 mm>
39.94 -40.00 mm
5mm
40.25 mm
40.5 mm
0.2 mm
EX side
12.004 -12.015
mm
11.996 -12.000 mm
Key stone
1.5 x 1.8
mm
0.15 -0.35 mm
0.03 -0.05 mm
- 11 -
LBBO IIAC
47.00 -47.02 mm
f-
f-
46.94 - 47 .00 mm
f-
47.25 mm
47.5 mm
0.5 mm
f-
f-
f-
f-
2.0 x 2.1 mm
f-
0.02 -0.06 mm

Model LB50 II AC LB80 II AC
2nd ring:
C]Js
I T I
Type Keystone -
Dimensions (8 x T)
1.5 x 1.8 mm
-
End gap (installed)
0.15- 0.35 mm -
Side clearance 0.03 -0.05
mm
-
2nd ring:
I
l]s
I T I
Type -Plain
Dimensions
(8 x T)
-
2.0 x 2.1 mm
End gap (installed) -0.15 -0.35
mm
Side clearance -0.02 -0.06
mm
Crankshaft: F
-
4~
E}D
A
Crank width "A"
37.90 -37.95 mm f-
Runout limit "C"
0.015 mm
f-
Big end side clearance "D"
0.20 -0.50 mm
f-
Big end radial clearance "E" 0.004 -0.015 mm 0.004 -0.017 mm
Small end free play "F"
0.8 -2.0 mm
f-
Automatic centrifugal clutch:
Clutch shoe thickness
2.5mm f-
<Wear limit> <2 mm>
f-
Clutch-stall revolution 2,800 -3,200 r/min 2,700 -3,200 r/min
Transmission:
Main axle deflection limit 0.015 mm f-
Drive axle deflection limit 0.015 mm f-
Kick starter:
Kick starter
type Kick and mesh type
Ratchet type
Kick
clip friction force 8.0 -20.0 N 8.0 -
15.0 N
(0.8 -2.0 kg) (0.8 -
1.5 kg)
- 12 -

Model LB50 II AC LB80 II
AC
Air filter oil grade: Form-air-filter oil or s--
SAE10W30 type SE
motor oil
Carburetor:
I. D. mark
2T5 00
1F5 01
Main jet
(M.J) #95
s--
Air jet (A.J) 2.5 s--
Jet needle (J.N) 3G9/3 s--
Needle jet
(N.J) E-4 E-8
Cutaway
(C.A) 2.5
s--
Pilot outlet
(P.0) 0.9 -1.5
s--
Pilot jet
(P. J) #17.5 #15
Air screw
(AS)
1 1-3/4
Valve seat size
(V.S)
1.2 s--
Starter jet (G.S.1) #20 #25
Float heigh
(F.H)
22.0± 2.5 mm s--
Engine idle speed 1,250 -1,450 r/min
s--
Reed valve:
Thickness 0.15
mm s--
Valve stopper height
6.8 -7.2 mm
s--
Valve bending limit
0.3 mm
s--
Lubrication system:
Autolube pump:
Plunger diameter 3.5mm 4.0 mm
Color code Grey
Brown
Minimum stroke 0.20 -0.25 mm 0.25 -0.30 mm
Maximum stroke 0.55 -0.65
mm
0.80 -0.95 mm
Pulley adjusting mark At idle s--
- 13 -

CHASSIS
Model
LB50 II AC
LB80 II AC
Steering system:
Steering bearing
type
Ball bearing r
No. I size of steel balls
upper 22 pcs I 0. 1875 in r
lower 19 pcs I 0.25 in r
Front suspension:
Front fork travel
75 mm
r
Fork spring free length 482
mm
r
Spring rate (K1) 8.45
N/mm
r
(0.845 kg/mm)
(K2) 18.0 N/mm (1.8 kg/mm) r
Stroke (K1) O- 48 mm
r
(K2)
48-75 mm
r
Optional spring No r
Oil capacity left
96 cm
3 r
right 120 cm
3 r
Oil grade Fork oil 10W
or equi- r
valent
Rear suspension:
Shock
absorber travel
65 mm
r
Spring free length
212 mm
r
Fitting length
207 mm
r
Spring rate (K1) 21.0 N/mm
(2.1 kg/mm) r
(K2) 28.5
N/mm
r
(2.85 kg/mm)
Stroke (K1) O- 34 mm
r
(K2)
34 - 65 mm
r
Optional spring
No r
Swingarm:
Free play limit
end 1 mm
r
side 0.5
mm
r
Front wheel:
Type Disc
wheel
r
Rim size 2.50C x 8 r
Rim material
Steel r
Rim runout limit
radial 1mm
r
lateral
1mm
r
Rear wheel:
Type Disc
wheel
r
Rim size 2.50C x 8 r
Rim material
Steel r
Rim runout limit
radial 1mm
r
lateral
1mm
r
- 14-

Model LB50 II AC LB80 II AC
Drive chain:
Type I
manufacturer DK420 I DAIDO DID420 I DAIDO
No.
of links 94 88
Chain
free play
20 - 30 mm
<c-
Front drum brake:
Type Leading,
trailing <c-
Brake drum inside diameter 110 mm <c-
<Limit> <111 mm> <c-
Lining thickness 4mm <c-
<Limit>
<2 mm>
<c-
Shoe spring free length 50.5
mm <c-
Rear drum brake:
Type Leading,
trailing <c-
Brake drum inside diameter
110 mm <c-
<Limit> <111 mm> <c-
Lining thickness
4mm <c-
<Limit>
<2 mm>
<c-
Shoe spring free length 50.5 mm <c-
Brake lever & brake pedal:
Brake
lever free play (at pivot)
5-8mm <c-
Brake lever free play (at lever end)
10-20mm <c-
-15-