ATK 1988 250 User manual


Pre-Ride Inspection
Break-In Period
Fuel
and
Oil
White
Poter
Forks
TABLE
OF
CONTENTS
a. Routine
Maintenance
b.
Oil
Replacement
c.
Fork
Schematic
d. Spring
Rate
e.
Pre-Load
Adjustment
Rear
Shock
a.
Suspension
Sag
b. Spring Rates Available
c.
C~ression
Dampening
d.
Rebound
Dampening
Drive
Chain
a.
Chain
Tension
b.
Maintenance
Brakes
.a.
Rear
BraK~
Adjustment
b.
Rear
Reservoir Fluid level
c.
Rear
Brake
Pads
d. Front Reservoir Fluid
Level
e.
Front
Brake
Pads
f.
Bleeding the Front
and
Rear
Brakes
Air
Filter
Engine
Maintenace
a. Clutch Adjustment
b.
Transmission
Oil
Change
c. Ignition
Timing
Spark
Plugs
Carburetor
Engine
Clearances
a. Piston
Ring
End
Gap
b.
Piston to Cylinder
c.
Compression
Ratios
Torque
Specifications
Technical
Data
Special
Tools
PAGE#
1
1
2
3,4.
I 5
6 I 7
8
9 &
10
11
12 &
13
13
14
15
16
17
18

PRE
RIDE
INSPECTION
Before
jumping
on
yo~r
machine
and
blasting around, take caution
and
check
the condition
of
some
important items.
1.
Be
sure
throttle
is
free
and
that
ft
will snap
back
to
a
closed
position.
2.
With
the engine running, see
if
the Kill-Button
will stop
the
motor.
3.
Will
the brakes stop the wheels?
4.
Is
the chain adjusted correctly?
5.
The
air
pressure in the
tire's
should
be
141bs1n the
front
and
10-12
lbs
fn
the
rear.
6.
Turn
fuel petcock
lever
to the
on
position.
NOTE:
Cl'ose
to
off
position
when
not in use.
7.
Read
the
rest
of
this
operators manual!!
BREAK
IN
PERIOD
A
little
bit
of
care in the
way
you
treat
your mqtorcycle during
its
initial
operation, will
reward
you
with extended
life
and
increased
performance.
·in the
first
THREE
HOURS
of
operation, the engine should not be subject
to
excessiveand prolonged
RP.M
nor extreme loads.
In
other
words
Do
Not
Lug
the
motor
down
nor
Rev
for
extended periods.
During
the break
in
period, adjustments
may
be necessary
to
the
clutch,
throttle,
spokes, drive chain,
and
nuts
and
bolts.
Both
front
and
rear
brakes require a seating in process
of
the pads
to the disc.
1

Fuel
and
Oil
Operate your
ATK
with the best fuel
you
can
obtain. lie reccmencl (92
Octane)
unleaded
premi1111
at
the correct
oil
mixing
ratio.
Never
experiment with methanol, naphtha. or similar productl
.._td
Ocune
Boosters completely.
Use
instead.
all
or part
Race
or
Awtaftflf:-tU!T lllixJ.
When
selecting
an
oil
to
mix
with
your
gas,
use
a high qualttJ
2 cycle
oil.
Mix
the
oil
according to manufacturer recaamendattons
on
the container.
Rec011111ended
Fuel
Ratios:
250---40 to 1.
406---32 to 1.
Note:
When
using pre-mixed
fuel.
shake
the container throughly as
the
oil
might
settle.
Never
use
an
open
flame
to
check
the fuel level.
Gasoline
is
flanmable
and
explosive
under
certain conditions.
Do
not
add
fuel while engine
is
running.
2

Mhite
PC*er
Upside
Down
Forks
Routine
Maintenance
To
achieve
the
best
performance
fram 10ur
forks.
follow._
mUelfnes.
1.
Release
any
air
pressure
that
my
buildup
after•
an<llrd
.i
rlding.
2. Pull
the
fork wipers
down
and
clean
around
the
seal
......
.tar
a build-up
of
df
rt
accurs.
3.
Change
the fork
of
1 every
fifty
hours
of operation or
ldlen
damping
becomes
erratic.
on
Replacement
1.
Re
1ease
any
a
fr
pressure
t;ui
1
dup.
2.
Loosen
top
and
lowr
fork caps before
removal
from
the
•chfne.
3.
Remove
the front wheel.
brake
caliper assy.
and
brake
line
guides
and
lay
back
at
sf
de
of
machine.
4. Pull forks
from
machine.
invert
and
unscrew
inner tube fork cap.
Remove
preload spacer (1f
fitted)
and
fork spring.
5.
Drain
the
oil
out
and
replace spring.spacer
and
cap.
6.
Tum
the
fork over and
unscrew
top
ap.
Compress
fork
sl
fghtly to
remove
the
half
moon
.washers.
7.
To
remove
the keeper
below
the washers. press
on
onesfde
and
compress
fork.
8. Pull out the
remaining
bottom
out buffer
and
nylon
spacer. Drain
any
remaining
oil.
9.
llhen
compressing
the fork the
dampening
rod will extend out of the
fork
and
inside the
bypass
valve
vill
come
into clearer
vfew.
Fork
Schematic

10.
This
bypass
valve
has
six
holes in
it
with a
shim
on
the other side
that
must
be
opened
to
all°"
the
oil.to
pass.
You
must
do
this
when
re-filling
or
bleeding
air
out.
Use
a
long
rod
1/8• d;ameter
or
less
to depress the valve thru
one
of the holes. This allows the
oil
to
drain
down
into the lower fork leg.
11.
Pour
in approximately
18-21
ounces
of
Bel-Ray
HVI
lOW
shock
and
fork
oil.
12.
To
bleed the
air
from
the inner tube
you
must
keep
the valve
open
for
about 3 minutes.
Wait
till
there are
no
more
air
bubbles in the
on.
13.
The
standard
measurement
of the
oil
level
is
when
the
damping
rod
is
extended (12Qmn)
from
the fork tube, yet
at
the
same
time keeping
the
oil
level flush with the bleed valve
(Bypass
valve.)
14.
Quantity of the
oil
in the fork affects only the
last
fifty
percent
of the
travel.
More
oil
in the fork will
result
in
less
tendency to
bottom
out.
15.
Never
exceed
an
oil
level height of
l30mm
and
never
go
below
lOOmm.
HAL,r-MOON~
,-
WASNEAS
I c
KEEPE~~
,-------f
a4MPEN#\/G
ROI)
\Oo-t1o--.
EXTENSION
LENGTH
I
~·~
o\\
~
BOTTOM-01/T~
Bll.l'".l'"EIR
"=::=7
NYLON~I
SPACEI?
~
l<OLJ
LJEPRESSING
BYPASS
YALYE
~·~
i--
______
t
__
-----
-"-\id~\\d,
FIGURE
I
4
OVTER
FORI<
Tt./B£9
BLEEO
l//4t.YE

PRELOAD
AD.JUSDDT
To
change
the
tn1tta1 stage
of
travel
_t~
•
tire
:
-~
-
_
decrease
or
extend
the
length
of
the preload spacer.
B.y
dic,..stlj.jhe
1ength
.r
the
preload. the
softer
the
tnftfal
travel will
lie.
Ste
ftgure
for
freload
measurement.
PRELOAD
LENGTH
0
Inch
(Ollln)
1/8
Inch
(~i)
1/4
Inch
(&am)
FIGt/RE
~
FIGURE
2
EXAMPLE
SPRING
RATE
FORK
ACTION
Ll6HT
MEDIUM
HEAVY
If
increased
bottoming
is
noticed.then front fork springs are too
light.
An
optional
ATK
Multi-Rate
Fork
Spring Kit
is
available in a
23-25
lb
range
through your
ATK
Dealer.

REAR
SHOCK
REAR
SUSPEl•SIOH
SAG
The
rear suspension should sag 2-3 inches
(51-7&mn)
when
sitting
on
the
bike in
nonnal
riding position. This small sag requirement
is
due
to the
A-Trak
chain torque elfminaf:t'r,
which
increases in usable
rear
suspension.
From
our experience
we
recomnend
that
for
motocross racing
2-23f
inches
(51-64nm)
of
sag
is
best .For
trail
riding
use
up
to 3 inches.
Prop
the bike
up
on
a center stand
so
that
the
rear
wheel
is
off
the ground,
thus unloading the
rear
spring of the bikes weight.
Measure
the distance
between
the center
of
the axle to the center
of
the
left
side
na.noer
plates
rear
attactunent screw as
shown
on
figure 4. This distance
is
the extended
travel length.
Take
the bike
off
the stand
and
sit
on
it
in your
normal
riding positon.
Measure
the
new
distance
between
the center
of
the axle
to the center
of
the
left
side
number
plates
rear
attachment screw. This
distance
is
the usable travel length. Subtract the usable travel length
from
the extended travel length
and
the difference
between
the
two
is
the
suspension sag.
EXTENDED
TRAVEL
LEl~GTH
-
USABLE
TRAVEL
LENGTH
EXffNL)ELJ
LENGTH
'OMPRESS£0
~£'NGTH
l
F/Gt/l?E
~
=
SUSPENSION
SAG
CONPllESSION
ALJJf/STE,4
Pl<£L0Af)
AtJ./l/STEll
t t
COMPl?ESSfLJ
LENGTH
'
F!Gt./l?E 5
To
achieve your desired suspension
sag
it
will be necessary to adjust
the
rear
shock's preload as
sho~n
on
figure 5.
The
preload equals the
free
length
of
the
rear
spring
minus
the compressed length
of
the
spring.
FREE
LENGTH
-
COMPRESSED
LENGTH
=
PRELOAD
6

The
standard
free
length
of
the
rear
spring
is
8 11/16 inches
(22~).
This length
can
vary
slightly
from
spring
to
spring.
The
preload should
be
adjusted
to
~ithin
o•
and
112•.
The
preload
must
never exceed 1/2 inch
(l~).
If
the preload
falls
out
of
the 0-1/2 inch
d1me~s1ona1
boundary
vhile
obtaining the 2-3 inches
of
suspension sag. a heav1er
or
lighter
spring
rate
ts
necessary.
EXAMPLE
SAG
PRE
LOAD
COlltENTS
2•
(SOmm)
1/8
6000
GOOD
3•
(76mm)
0
3• (76mn)
5/s•
(1611111)
HEAVIER
SPRING
RATE
NEEDED
2•
(50Dln)
0
LIGHTER
SPRING
Kg/11111
LB/IN
7.8
435
REAR
SPRING
RATES
AVAILABLE
8.2
460
8.7
485
COMPRESSION
DAMPENING
9.2
515
RATE
NEEDED
The
compression
dampening
adjustment
knob
is
shown
on
figure 5. There
are seven compression
settings
to choose from.
Turn
the
knob
counter
clockwise
until
it
stops,
at
this
position the compression
dampening
is
set
at
the
softest
rate.
To
increase compression
dampening
turn the
adjustment
knob
clockwise
one
setting
(click)
at
a time.
There
is
no
standard
setting
for
the compression dampening. Track
conditions
and
each
riders
ability
detennines
this.
From
our racing
experience
we
recomnend
that
you
set
the compression
dampening
between
one
thru four.
REBOUND
DAMPENING
The
rebound
dampening
adjustment
wheel
is
located under the spring
retainer
as
shown
on
figure 5.
There
are eleven rebound
dampening
settings
to
select
from. Setting
one
is
the weakest absorbtion--
the
shock
absorber extends
fast
after
compression.
Setting
eleven
is
the strongest absorption
position--the
shock
extends
slovly
after
compression. Like the compression
dampening,
the rebound
dampening
does
not
have
a standard
setting.
7
9.7
540

DRIVE
CHAIN
CHAIN
TENSION
Shift
the transmission into neutral.
Check
the slack in the upper
drive chain
midway
between
the
A-Trak
top
roller
and
the
rear
sprocket.
Drive
chain slack should be adjusted to allow 1 3/4 inch
(44111)
vertical
•ovement
by
hand
as
shown
on
Figure 6. This
minimal
slack requirement
is
due
to the design characterist1c
of
the
ATK
chain torque eliminator.
CHAIN
MAINTENANCE
The
drive chain should be checked, cleaned,
and
lubricated
after
every
ride.
Never
use
an
engine degreaser or solvent
on
the chain to clean
it,
this
may
aamage
the rubber o-rings.
When
lubricating the chain
always
use
a lube designed
for
o'ring
chains.
The
A-Trak
chain torque eliminator
rollers
are maintenance free.
r/GUl?E
6
4-1
FIGURE
6
8

Rear
Brake
Adjustrr.ent
The
countershaft
disc
rear
brake
is
the
most
effective
stopping system
ever designed.
Applying
the brake has
no
effect
on
the suspension. Therefore. those
riders
who
steer
with the rear brake or drag the
rear
brake
will
cause
the brake
fluid
to
heat up,
which
will
cause excessive
pad
wear.
llOTE:
DOH'l
DRAG
THE
BRAKE---SLOWING
ONLY
AP-Lockheed
Racing
fluid
used in race cars
is
a higher temperature brake
fluid,
which
is
an
alternative
from
the standard
DOT-5
brake
fluid.
Pedal
height
is
important. Adjust the pedal
tip
low
enough
below the
operators boot so
that
it
will not
be
applied unknowingly.
free Play adjustment between the Master cylinder
piston
and
actuating
rod should never
be
nonexistent, (1/16"
to
1/tin.)
~i°';
~
tLr
~'~
..a1r//.UM..l'I
_____
?\~s~c...
~t.r
Rear
Brake
Reservoir Fluid
Level
Keep
the
fluid
level
of
DOT
5 topped
up
at
all
times.
Remove
Allen screw
cap
at
top of
reservoir
and
fill
to
the
2nd
thread
in
filler
hole.
Rear
Brake
Pads
The
brake pads should
be
checked
after
every
Race
or
Ride.
MinillUll'I
pad
thick-
ness
is
1/168 (I.Sam). ·
Br~ke
pads are
easily
replaced
by
popping
plastic
cover
off
with a small screw-
dr1ver.
Rt;move
cotterpin
from
retainer
pin (
this
is
located
on
the
back
side
of
the
cahper).
Pull
retainer
pin.
Pads
may
now
be
replaced.
Note:
On
reinstallation
of
retaining pin use a
new
cotter
pin
and
secure properly.

BRAKES
HYDRAULIC
BRAKE
MAINTENANCE
FRONT
BRAKE
FLUID
Fluid level should
be
approximately 1/8 inch
(Jan)
below
the
edge
of
the reservoir
when
refilling.
Never
let
the
fluid
level get
below
the visual indicator.
When
refilling
use
DOT
5 hydraulic
brake
fluid.
FRONT
BRAKE
PADS
Pad
thickness should
be
no
less
than 1/16 inch
(1.511111).
If
pad
thick-
ness
is
less
than 1/16 inch, replace
by
removing
pad
retainer
pin.
BLEEDING
THE
BRAKE
If
air
is
sucked
into
the hydraulic system
due
to
low
fluid
leV!l
or
a
break in the brake
line
occurs,
it
is
neccessary to bleed the system
in order to purge the
air
out.
Check
the level
of
fluid
in the reservoir
and
top
up
if
required.
Remove
the dust
cap
from
the bleed screw. Attach a rubber
hose
of
internal diameter
of
1/4 inch
(&rm)
and
approximately
24
inches
(610mm)
in length
to
the
bleed·
sere-.
Place the
end
of the
hose
in a glass
jar
filled
with approximately
1 inch
(25mn)
of
hydraulic
fluid.
Make
sure
that
the
end
of
the
hose
stays
submerged
in the hydraulic
fluid
thru the
entire
b1eed process. Activate
the brake lever several times
and
hold in the braked position. Continue
this
operation
until
no
air
bubbles
can
be
seen
coming
from
the hose.
At
intervals
make
certain
that
the reservoir
is
kept topped up, otherwise
air
will
enter
the system again.
10

Air
Filter
The
unique
snorkel
air
intake
has
been
designed to
minimize
the
impact
of dust.
mud.
and
water. yet increases
its
ability
to
receive
an
abundant
amount
of clean.
cool
air.
Responsiveness
of the
Rotax
motor
has
been
increased
due
to the
high
vol1111e
still
air
chamber.
Due
to the
Kll~'s
extreme
amount
of
air
flow
capab111tes,
(3
times
more
surface area)
combined
with
its
location
on
the motorcycle,
cleaning the
filter
is
not required as often.
Read
Below
Instructions Carefully!!
AIR FILTER SERVICE INSTRUCTIONS
1.
PRE-CLEANING
Tap
the
element
to
dislodge
any
large
embedded
dirt.
then
gently
brush
with
a
soft
bristle
brush.
(Note
:
If
complete
clean-
ing
is
not
practical at
this
time.
re-oil
the
element
and
re-install
in
your
vehicle.)
4.
CLEANING
HINTS
Use
only
KIN
air
filter
cleaner
.
NO
gasollne
cleaning.
NO
st11m
cleaning.
NO
caustic
cleaning
solutlans.
NO
strong
d!lergems
.
NO
high
pressure
car
wash.
NO
parts
cl11nlng
solvents.
Any
of
these
NO's
can
cause
harm
to
the
cotton filter
media.
plus
shrink
and
harden
the
rubber
end
caps.
1.
AEROSOL
OILING
After
cleaning
air filter
always
re-oil
before
using.
Spray
KIN
air
filter
oil
down
into
each
pleat
with
one
pass
per
pleat.
Walt
10
minutes
and
reoll
any
white
spots
still
showmg.
2.
SPRAY
ON
CLEANER
Spray
KIN
air
filter
cleaner
liberally
onto
the
entire
element
and
let
soak
for
10
minutes.
5.
RINSE
OFF
Rinse
off
the
element
with
low
pressure
water
.
Tap
water
is
OK.
Always
flush
from
the
clean
side
to
dirty
side.
This
removes
the
dirt
and
does
not
drive
it
into
the
filter.
'I
II I I
J
•••
'
8.
SQUEEZE
BOTTLE
OILING
After
cleaning
air
filter
always
re-oil
before
using.
Squeeze
K&N
air
filter
oil
down
into
the
bottom
and
along
each
pleat
-
only
one
pass
per
pleat.
Let
oil
wick into cotton for
20
minutes.
Re-oil
any
white
spots
still
showing
.
3.
PAN
CLEANING
Large
KIN
elements
can
be
rolled
or
soaked
in
a
shallow
pan
of
KIN air filter
cleaner.
Remove
immediately
and
let
soak
for
approximately
10
minutes.
6.
DRYING
HINTS
Always
dry
naturally.
After
rinsing.
shake
off
the
excess
water
and
let
the
element
dry
naturally
.
DO
NOT
USE
COMPRESSED
AIR
DO
NOT
USE
OPEN
FLAME
DO
NOT
USE
HEAT
DRYERS
EXCESS
HEAT
WILL
SHRINK
THE
COTTON
Fil
TER
MEDIA.
COMPRESSED
AIR
WILL
BLOW
HOLES
IN
THE
ELEMENT.
9.
OILING
HINTS
Never
use
aKIN air filter
without
oil.
(The
filter will not
stop
the
dirt without
the
oil.)
Use
only
K&N
formulated
air
filter
oil.
K&N
air filter
oil
is a
compound
of
mineral
and
animal
oil
blended
with
special
poly-
mers
to
form
a
very
efficient
tack
barrier.
Red
dye
is
added
to
show
just
where
you
have
applied
the
oil.
Eventually
the
red
color
will
fade
but
the
oil
will
remain
and
filter
the
air
.
NEVER
USE
Automatic
Transmission
Fluid.
NEVER
USE
Matar
011.
NEVER
USE
Diesel
Fuel
.
NEVER
USE
WD-40.
LPS.
or
other
llght
weight
alls.

ENGINE
MAINTENANCE
CLUTCH
ADJUSTMENT
If
you
feel major adjustment
is
required , loosen the clutch
adjustor
at
the handlebar
to
provide
maxima.an
slack
of
the cable.
Remove
the clutch adjustment access plug
on
the
left
sidecover. There
is
an
llmm
lock nut
and
a
slotted
adjusting screw.
NOTE:
Special
wrench
is
provided in the tool
kit
to
loosen the
11.nln
locknut.
Turn
the
slotted
adjusting
screw
in until contact
is
made
with the release
bearing.
Then
turn out
1/8
-1/4
turn
from
the contact point.
Carefully retighten the
llmm
lock nut to secure the clutch adjustment.
Replace
the access plug.
TRANSMISSION
OIL
CHANGE
Start
the engine
and
allow
it
to
wann
up
briefly.
Remove
the
6mm
Allen
head
bolt
from
the
bottom
of
engine
and
completely drain the
oil.
NOTE:
Don't
remove
the
17nun
bolt
head
kickstart
spring retaining
bolt.
The
drain plug
tip
is
magnetized
and
should
be
cleaned
of
metal
particles
before
installing
the drain plug.
Remove
the
filler/vent
plug
and
refill
the transmission with
lOOOcc
(32
US
oz)
of
a
li
ht
viscosit
ear
oi until the
oil
reaches the
oil
level
(&nm
allen
bolt
inspection hole.
The
level plug
is
located
behind
the gear
change
lever.
Examples
of
Light Viscocity
Gear
Oils:
Bel-Ray
Light Viscosity
Mobil
1
75W-80
Amsoil
75W-80
Silkolene
Gear
oil
Light
75W
Dura
Lube
Gear
and
trans
oil
LV
There
are a
number
of
other Light Viscosity
Gear
oils
on
the market,
this
list
is
meant
as a
partial
example
of available products only.
In
a pinch
20W-50
Motor
oil
may
be used.

IGNITION
TIMING
Your
motorcycle
is
equipped with a capacitor discharge
ignition
which
consists
of
a magneto,
an
electronic
control
unit
and
a Kill-Button.
Regularly check the
electrical
connections
for
dirt
or
corrosion.
Apply
a
dielectric
grease
to
all
connectors
and
the high tension lead
when
necessary.
Timing
of
the engine
can
only
be
done
with a stroboscopic
lamp.
Although
timing
marks
can
be
verified
by
using a dial
indicator.
Static
timing
figures are as follows:
250:
14°±
1,
1.07
nm
(0.042in)
406:
18°±
1,
2.26
nm
(0.089in)
On
all
machines
remove
the timing inspection plug
from
the
magneto
cover
and
connect the timing
light
pickup
to
the high tension lead.
Point the
light
beam
straight
into the inspection hole
and
rev the engine
to
5000
RPM
for
a
brief
instant.
If
the timing
is
correct
the
magneto
cover
mark
and
flywheel
mark
will align with each other.
If
timing
was
incorrect,
remove
magneto
cover.
Loosen
the
stator
retaining
screws then
move
the
stator
plate
in the advance
or
retarded
direction
to
correct the misalignment. Tighten the
stator
plate
screws.
Start
the engine to recheck the alignment
of
the timing
marks
with the
timing
light.
ATK
250
406
88ES
BSES
SPARK
PLUGS
Reco11111ended
Plugs
Bosch
W275T2
W275T2
TO
CHECK
CONDITION-
OF
SPARK
PLUG
A
Brownish
tip
reflects
correct
jetting
and
plug range.
A black
insulator
tip
indicates a rich condition.
Auto
Lite
I
4053
I
4053
A grey
tip
warns
you
of
too lean
an
operating temperature.
Advanced
ignition
timing, engine overheating, fuel mixture too lean, clogged
carburetor
jetting,
wrong
spark plug heat range
or
a leaking seal
or
gasket.
13

M'KUN'
Performance
Starts Here
RACING CARBURETOR$
TMXBERIES
TMX35and38
S'\<>d<
tSo
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"'o~
MIKUNI
TMX
SERIES
PARTS
UST
No.Description
1
MIXING
BODY
CARB
2
JErNEEDLE
I
COVER.
CARS
TOP
4
LQCK
NUT,
ADJUSTER
5
CAP,
RUBBER
6
~A.CABLE
7
().RING,
TOP
COVER
8
E-RING,
NEEDLE
CUP
9
RING,
RETAINING
10
ADJUSTER,
IDLE
STOP
11
SPRJNG,
IDLE
ADJUST
12
PLUNGER,
STARTER
ASSBLY
13
SCREW,
AIR
ADJUSTER
14
SPRING,
AIR
SCREW
15
CHAMBER.
FLOAT
BOWL
16
VALVE
SEAT.
NEEDLE
17
PlLOT
JET
18
MAINJET
19
ARM,
FLOAT
20
NEEDLE
VALVE
ASSBLY
21
PIN,
FLOAT
ARM
22
().RING,
NEEDLE
VALVE
23
CAP,
FLOAT
RETAINER
24
SCREW,
TOP
COVER
25
THROTTLEVALVE
26
SPRJNG,T.V.
27
HOSE,
VENT
28
SCREW,
FLOAT
BOWL
29
HOSE,
OVER
FLOW
30
FLOAT,
LEFT
SIDE
31
().RING,
DRAIN
PLUG
32
DRAIN
PLUG
.
33
FLOAT,
RIGHT
SIDE
34
GASKET,
FLOAT
BOWL
Part Number
1M38SS11
•SEE
TUNING
77&19014
830/247
VM34/282
VM30f77
11&93009
8532/126
TM38/54
803-25008
N110209
TM38/57
803-36002
VM15/112
TM38/48
8&26002·3.5
VM22/210
4/042
VM36/15
788-26005
VM20/315
KV/10
YM26/42
CW2•0412
832-41002
730-13019
188-24Q11
CW2-o308
888-23022
859-52021
VM28/254
TM38/44
859-52020
TM38/52
a-·
.
~·-2
-g
12
11.J.
350
--
N.
6£N1-S3
--P.J.
15
t1.J.
370
--
N.
6£J12-S7 --P.J. IS
·~
2

ATK
250
406
ATK
250
406
ENGINE
CLEARANCE
PISTON
RING
END
GAP
STANDARD
0.20 an (0.008 in) -0.35
mm
(0.014in)
0.25
1111
(0.010 in) -0.40
am
(0.016in)
PISTON
TO
CYLINDER
CLEARANCE
STANDARD
0.06
11111
(0.002 in) -0.08
nm
(0.003 in)
0.08
mm
(0.0~3
in) -0.09
nn
(0.0035 in)
SERVICE
LIMIT
1.0 m (0.0401n)
1.2 m (0.047in)
SERVICE
LIMIT
0.14 -(0.005
0.18
DID
(0.007
Increased perfonnance
can
be obtained
by
changing compression
ratios
on
the 250.
and
406.
The
chart
below
can
be
used
as a guide to your fuel
needs.
250
Com2ression
Ratio
Fuel
Requirement
12.5:1 Stock
Unleaded
Regular
Remove
1
head
shim
13.0:1
Mod.
Unleaded
Premium
Remove
2
head
shims
13.5:1
Mod.
100
L1
Aviation
406
Com2ression
Ratio
Fuel
Reguirement
4x0.2
mm
shims
10.0:1 Stock
Unleaded
Regular
Remove
3
shims
10.8:1
Mod.
Unleaded
Premium
Remove
4
shims
11.0:1
Mod.
100
LL
Aviation
15

TORQUE
SPECIFICATIOHS
Part
fjame
Front axle
Front axle pinch
Rear
axle nut
Swing
arm
pivot nut
Triple
clamp
allens
Engine
mount
Flywheel
nut
Clutch
hub
nut
Primary drive nut
Countershaft nut
Cylinder
head
nuts
8mm
Cylinder
head
nuts
lOnm
Shock
eye
bolts
Torque
(ft.
lb)
30
6-8
65-75
65-75
15-20
25-30
65-75
60-70
68-78
40-50
16-18
26-26
30-35
The
table below,
relating
tightening torque to thread diar;.eter
and
pitch,
lists
the basic torque for the bolts
and
nuts
on
ATK
motorcycles.
Diameter
{mm)
ft.
lb.
5
2.5-3.5
6 4.5-5.5.
s 10.0-13.5
10
19.0-25.0
12
30-45
14
55-75
16
80-120
18
120-160
20
160-240
16

Technical
Data
ATK
250. 406
250
406
Displacement 248.4cc
399cc
Bore
and
Stroke
72x61
lllH
84x72
m
Gear
Ratios J.-3,000:1 1-2.384:1
2-2,070:1 2-1,769:1
3-1,571:1 3-1,400:1
4-1,353:1 4-1,116:1
5-1,222:1 5-0,913:1
6-1.150:1
Compression
Ratio 12.5:1 10.0:1
C/S
Rear
sprocket 15/50 15/50
Ignition Motoplat •totoplat
Carburetor Keihin Keihin
Chain
520
520
Oil
Capacity
lqt.
lqt.
Afr
Filter
K&N K&N
Weight
208
216
Steering
Angle
27°
27°
Uheelbase
57
11
57•
Seat Height
37"
37a
Ground
Clearance
14
11
14
11
Fuel
Capacity 3.0 gals 3.0 gals
Front
Fork
11.sa 11.&n
Rear
Shock
12.0 12.0
Front
Brake
4-Piston Caliper
Disc
Rear
Brake
2-Piston Caliper
C/S
Disc
Front Tire 3.00-21• 3.00-21•
Rear
Tire
110-100x18
110-100xl8
Fork
Capacity
650
cc
650
cc
Shock
Pressure
1801bs
1801bs
17

Ref.
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
13
Special
Tools
Description
Seal
insertion
jig
(clutch cover)
Seal
insertion
jig
(tranny
main
shaft
406)
Seal
insertion
jig
(tranny
main
shaft
250)
Seal
insertion
jig
(crankshaft clutchside
250)
Plastic
Ring
insertion
jig
clutch side
Plastic
Ring
insertion
jig
mag
side
Pu
11
er
assy.
Clutch
hub
locking tool (old
style)
Clutch
hub
locking tool
(new
style)
Protection
Cap
Guide
sleeve for
oil
seal
(main
shaft)
Crankshaft locking bolt
Flywheel
puller
Bearing
puller
Hexagonal
screw
Allen bolts
Clutch adjustment
wrench
Crankcase
separator
puller
Slotted
head
screw
Half ring for puller
Ring
for puller
Puller plate assy.(crankshaft)
El
§
iC
II
18
'
IZ
>
•
'1
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