Mercury 1976 340 S/T, 1976 440 S/T Service Bulletin

Number: 76-9

CIRCULATE

TO:

GASOLINE/OIL RECOMMENDATIONS -

ALL MERCURY SNOWMOBILES

(Atwch

IMPORTANT: Supersedes all information previously published
line/oil recommendations: Service Manual, Operation and Maintenance
Manuals, Snowmobile Service Bulletins and "Fuel Warning Tags- Posters".

Recommended Oil(s)

Quicksilver Snowmobile
Quicksilver Formula 25 50:1

Quicksilver Formula
Quicksilver Formula 50 50:1

BIA!TC-W Rated

Bulletin Reference Sticker to

Fan Cooled and Free-Air Models

Ratio (1)

50:1

500

50:1

40:1

SNOWMOBILES

SERVICE MGR. PARTS MGR.

Page

1-6

of

Your Snowmobile Service Manual.)

Fan

Cooled

Gasoline (2) Ratio Gasoline (3)

Regular
Leaded

Motor

86

Octane)

Minimum

Average Octane

(80

20:1
20:1

20:1
20:1
20:1

Date :

MECHANICS

on

gaso-

Free-Air

100/130
AvGas

12/1/75

Place in Your

"Service Bulletins

Binder

(1) Ratio

(2)

(3)

of

25:1

is required

for

"Severe Service" operation. Refer
Service" definition.
For

1975

Model440
ignition
For
BTDC.
BTDC.

timing

Racing,

For

is retarded

use

100/130 AvGas and retard ignition

Trail Ride,

for

the

TIT

(Below CHASSIS Serial No. 4210250),

from

use

PREMIUM

first

.095"

(one)

tank-full

to

;,/Operation and Maintenance

BTDC

and retard

to

during engine

.080"

BTDC.

ignition

timing

timing

"Break-In"

use

from

.100"

from

PREMIUM, UNLESS

.100"

Liquid Cooled Models

Recommended Oil(s)

Quicksilver Formula
Quicksilver Snowmobile Oil

Quicksilver Formula

BIA!TC-W Rated 16:1

50

500

IMPORTANT: Some 1976 S/T "Operation and Maintenance Manuals
(C-90-74530)" recommended Quicksilver Snowmobile Oil, Quicksilver Formula
500

and BIA!fC-W Oils (all prediluted)

at

oils, ONLY,

a 16:1 ratio are permissible. CHANGE any

at a 20:1

the above recommendation (16: 1 ratio).

Liquid Cooled
Ratio Gasoline
20:1
16:1
16:1

ratio. Use

100/130 AvGas

of

these prediluted

of

these Manuals

period

Manual"

BTDC

BTDC

to

for

to

to

and/or

;,/Severe

.080"
.060"

~I:KYI~~

BULLETIN

TIIEI#'L

~~P.J

6 .....

n

~-=·

oe

wt"•"d""'

-KO

SNOWMOBILES

CIRCULATE

TO:

ZIN'Y

SERVICE MGR. PARTS MGR.

Date :

MECHANICS

r:

/tS-Tz-

12/15n5

Place

in

"Service Bulletin!

Your

Binder

A. Balancer Installation- 1976 Model340
B.

Driv

e Clutch Weights-

C.

Driv

e Outch Weights-

D. Lower

A.

BALANCER

(Attach Bulletin Reference Sticker

INSTALLATION

For
For

Cowl

ALL

ONLY

and Snow Flap Fasteners· All1976 Model250-340-440 Sno-Twisters

- 1976 Model

on

Section

1976 Model

1976

340

Model440

IMPORTANT: ALL 1976 Model250

ALL 1976 Mercury Sno-Twister Snowmobiles

[ 3.96mm] thick by

5.250"

[l3.34cm]

AU

1976 Model340

AU

1976 Model440

2C

In.dcx

S(f

S(f

SIT

diameter) between the rewind starter cup and lower pulley.

Strand

340

S(f

Page

(CHASSIS Serial No. 4495560

(CHASSIS Serial No. 4349537

440

Str

Snowmobiles
Str
Str

and 440 S/T Snowmobiles

of

Your Snowmobile Service Manual.)

and

and

Above)

already are equipped with the balancer.

MUST

BE equipped with a balancer (steel disc

Below)

The balancer (D-75961) stabilizes the crankshaft and prevents excessive vibration of the drive
clutch, thereby improving the life

IMMEDIATELY notify owners

MUST

BE INSTALLED (installation instructions following).

of

drive clutch components.

of

the above specifi

ed

Sno-Twister Snowmobiles

that

this balancer

IMPORTANT: A simple visual inspection via the water pump belt channel in the bell housing
can verify whether-or-not the balancer has been installed.

.156"

Order the required quantity of balancers and 4 screws for each balancer from your parts
distribution source. Credit for the balancers. screws and 0.3 hrs. labor per snowmobile
upon receipt

Nos

.) may be used to cover service

INSTALLATION

l.

Remove rewind starter assembly.

2. Remove 4 screws which secure rewind starter cup and low

of

a completed warranty claim. One warranty claim (listing individual CHASSIS Serial

to

all snowmobiles.

C-75961

C-10-75967

INSTRUCTIONS

Balancer

Scre

(1

per Snowmobile}

ws

(4 per Balancer)

er

pulley

to

rotor. RETAIN the 4

will be issued

lockwashcrs from the screws and discard the screws.

3.

Inslall balancer between lower pulley and s
IMPORTANT: Failure

to

damage

the rotor and could alter ignition timing.

a. Place MACHINED side of balanc

to

use the 4 lockwashers

er

b. Install lockwashers (retained in Step 2) on 4

(C-92-32609)

to

threads

of

screws and reinstall starter rewind cup with screws.

tart

er rewind cup.

on

the 4

NEW

retaining screws

against lower pulley (toward engine).

NEW

screws, apply Loctite Type

will

result in

"A"

4. Reinstall rewind starter assembly.

(OVER)

B.

DRIVE

CLUTCH WEIGHTS-

ALL1976

Model340 SIT

(Attach Bulletin Reference Sticker on Section

ALL 1976 Model

340

Sff

Snowmobiles

drive clutch assembly (6 weights per clutch). Some 340

4495867 and Below) were shipped from the factory with
these ARE NOT LEGAL for "Stock
1976

Model 340

INSPECTION PROCEDURE
l.

Part No. stamped into perimeter

INCORRECT:
CORRECT : XXXX-988- or XXXX-989-

2. OR, visual inspection

Str

Snowmobiles to check the drive clutch for correct

XXXX

088

088 088

of

the Part No. on the weights thru vent holes in drive clutch cover,

2C

Index Page

MUST

of

Your Snowmobile Service Manual.)

BE equipped with

SIT Snowmobiles (CHASSIS Serial No.

#106

II"

class racing.

of

drive clutch cover, as follows:

To

remedy, IMMEDIATELY notify owners

#135

weights (D-71737) in the

weights in the drive clutch, and

#135

weights.

follows:

INCORRECT:
CORRECT :

IMPORTANT:

XXXX

XXXX

If

106 (Color- Red)

135 (Color- Black)

the weights are incorrect and must be replaced, REMOVE the drive clutch
assembly from the engine before attempting clutch disassembly. Removal and/or installation
the drive

clutch~

works best

-·

with the aid

of

an arbor press.

of

as

of

Credit for the weights and 0.5 hrs. labor per snowmobile

will be issued upon receipt of a completed

warranty claim. One claim (listing individual CHASSIS Serial Nos.) may be used to cover service

all snowmobiles.

D-71737 Weight-

C.

DRIVE

(Attach Bulletin Reference Sticker on Section

ALL 1976 Model

CLUTCH WEIGHTS-

440

Sff

ALL1976

2C

Snowmobiles

Model440

MUST
drive clutch assembly (6 weights per clutch). Some
4349543 and Below) were shipped from

ill"

these ARE NOT LEGAL for "Stock
1976 Model440 SIT Snowmobiles

INSPECTION PROCEDURE
l.

Part No. stamped into perimeter of drive clutch cover, as follows:

INCORRECT:

CORRECT :

2. OR, visual inspection

XXXX
XXXX

089

-989-

089

of

the Part No. on the weights thru vent holes in drive clutch cover,

class racing.

to

check the drive clutch for correct # 106 weights.

Index

#135

SIT

Page

of

BE equipped with

440

the

factory with

To

(6 per Clutch Required)

Your Snowmobile Service Manual.)

#106

weights (D-71717) in the

SIT Snowmobiles (CHASSIS Serial No.

#123

remedy, IMMEDIATELY notify owners

weights in the drive clutch, and

follows:

INCORRECT:

XXXX

123

(Color-

Yellow)

to

of

as

CORRECT :

IMPORTANT:

XXXX

If

106

(Color-

the

weights are incorrect and must be replaced, REMOVE the drive clutch

Red)

assembly from the engine before attempting clutch disassembly. Removal and/or installation
the drive clutch cover works best --with the aid

of

an arbor press.

of

Credit for the weights and 0.5 hrs. labor per snowmobile will be issued upon receipt
warranty claim. One claim (listing individual CHASSIS Serial

~os.)

may

be

used

to

all snowmobiles.

of

a completed

cover service

to

D. LOWER COWL

Snowmobiles

(4ttach Bulletin Reference Sticker

LOWER COWL

To be sure
that

th<>

6 aluminum rivets, which secure the cowl

and

that

the lowf'r cowl remains securely fastened

D-71717 Weight-

SNOW FLAP

FASTENERS-

on

Section

2F

Index

#106

Page

ALL

of

to

diameter head - 3 located inside lower cowl in a line on each side

STEEL rivets (Mercury Part

X 5

/8"

shank

SNOW FLAP

[15.9mm) diameter head with

. C-17-76047)

or

an equivalent steel riv

3/8"

r9.5mm) toY:!" [12.7mm] grip range).

No

Check the rivets which secure the snow flap and mounting

out

from pulling
has a
(13/64"

If
or

"backing"

[5.16mm] J.D. x

the

rivets arc

equivalent) with the backing washers.

thru the snow flap, make sure

washer on

not

equipped with these backing washers, remove and install new rivets (C-17-64817

<>ach

Y2"

[l2.7mm]

riv

et

(Mercury Part No. C-12-21273) or an equivalent washer
O.D. x

that

l/16"

the

(6 per Clutch Required)

1976 Model 250-340-440 Sno-Twister

Your Snowmobile Service Manual.)

to

the front crossmember,

the

front

crossmember (silver colored,
of

crossmember), be replaced with

et

str

ip

to the chassis.

"clinch"

[l.59mm]

end

thick).

of

(3/16"

the rivet (inside

we

[4.8mm]

To

prevent

recommend

the

5/8"

diameter

the

rivet

tunnel)

0

0

0

.J'

~I:KY

B

ULLETIN

l\;1:

MERCURY SNOWMOBILES with ARCTIC DRIVE CLUTCH

Internal Drive Clutch Component Information

TIIEH

~!!",&

I

~

701.11

Ul\lf•I'IC•

of

<WI$l.nd1t19

.......

CIRCULATE

TO:

SNOWMOBILES

SERVICE MGR.

PARTS MGR. MECHANICS

Number: 76-13

Date : 12/22/75

Place

in

"Service Bulletins

Your

Binder

"Stock"

MODEL

CHASSIS Serial No.

MERCURY PART
LAST

3 DIGITS

OUTSIDE

DRIVE

DRIVE CLUTCH WEIGHTS

DRIVE CLUTCH RAMPS

of

CLUTCH SPRING
Color
No.

of

Turns 3.9 3.9 3.9

Mercury Part No.

Color

No. Stamped on Weights

Gram Weight
Outside Diameter
Mercury Part No.

No. Stamped on Ramps
Drawing
Mercury Part No.

of

NAME

NO

. D-52-71571 D-52-71572 D-52-74255 D-52-74256 D-52-75098 D-52-75099 D-52·75100

of

NO. STAMPED ON

DRIVE

CLUTCH COVER

Ramp Profile

Drive

4207500 4206250 4347125 4347124 4495560 4495559 4349324

061

Blue Blue Blue Blue

C-24-71517

Red
0146·106 0146·105 0146-106 0146-286 0146·106 0146·135CD

5.958g 7.858g 5.958g 8.800g 5.958g

0.530" 0.598"
D-71717

None

Figure 1
D-71496

Clutch

1975 1975 1976 1976 1976

340

srr

Below Below Below Above Below Above

440S

062 077 080

C-24-71517 C-24·71517 C-24-71517 C-24-74992 C-

Black

D-71716 D-71717 D-74125 D-71717 D-71737

None 292 293

0

Figure 1 0

(!)

D-71496 (! D-74123 D-74124 D-75908 D-75177

Component

/T 340 TIT

Red

0.530"

Figure 3 Figure 4

440 TIT

3.9

Yellow

0.629"

Chart

1976 1976

25o

srr

081

Green

5.0 5.0

Red

0.530" 0.471"

None
Figure 5 Figure 6

340S!T

088

Green

24-74992 C-24-74992

Black

4.479g

None

CD

CD

440

srr

Above

089

Green

5.0

Red
0146-106

5.958g

0.530"
D-71717

None
Figure 6
D-75177

CD

Optional Clutch Ramps (D-74857A

Q)

A few 1976 Model
drive clutch weights. Weights stamped 0146-135 (D-71137)
clutches.

: :

..

-

ACTUAL

Figure 1. D-71496 Drive Clutch
Ramp Profile (1975

440

S/T)

SIZE

340

S/T

340

&

1,

Figure

SIT

snowmobiles were shipped from the factory

2)

are available

for

trail riding.

MUST

'

·'

ACTUAL

Figure
Clutch Ramp Profile (Trail Ramp
for

2. D-74857A1 Drive

1975

340

(OVER)

S/T

& 440 S/T)

SIZE

with

INCORRECT

BE

INSTALLED

/

in

these

/

/

l J

ACTUAL

Figure 3. D-74123 Drive Clutch

Ramp Profile (1976

SIZE

340

T/T)

ACTUAL SIZE

Figure
Ramp

4.

D-74124 Drive Clutch

Profile (1976 440 TIT)

ACTUAL SIZE

Figure 5. D-75908 Drive
Ramp

Profile (1976 250 SIT)

Cluttch

ACTUAL

Figure
Ramp
440 SIT)

6.

D-75177 Drive Clutch

Profile (1976 340 SIT &

SIZE

MODEL

Drive Clutch Elevation
Drive Clutch Modification
Drive Clutch Trail Ride

N.A. -

Full

Throttle

Engine
Increase

Engine

Decrease
Engine

Q)

Six

Not

RPM

RPM

RPM

NAME

Available

Gram Weight

light

Heavy

of

these

Kit

Kit

3.058g 0146-108

3.725g 0146-175

4.479g

4.958g 0146-107

5.958g 0146-106

6.992g

7.858g

8.800g 0146-286

weights are included

Drive

1975 1975 1976 1976

340

SIT

D-71712A1

Kit

D-71711A 1 U-71711A 1
D-74857 A 1

D-71712A 1

D-74857A 1 N.A. N.A.

Drive

No. Stamped Outside Diameter

on Weight

CD0
CD0CD

0146-135

CD0CDCDCD
CD

CD

CD

CDCD

0146-123
0146-105

CD0CD
CD
0

in

Clutch

440S/T

D-74124A 1

Clutch

Drive Clutch

Accessories

1976

250

340

TIT

N.A. N.A. D-71711A2

Weight

Color

Modificat~on

D-i11716A 1

of

Weight

Yellow

Red

Black

White

Red

Yellow

Black

Yellow

440

TIT

Chart

I

Kit

of

0.406"

0.437"

0.471"

0.491"

0.530"

0.568"

0.598"

0.629"

(D-71711 A 1

SIT

D-71712A2

N.A. N.A.

Weight

1976 1976

340

S/T
D-71712A2 D-71712A2
D-71711

D-71731
D-71735
D-71737
D-71736 Q)

D-71717
D-71734
D-71716
D-74125

CD
CD 0 CD
CD

CDCD

CD0CD

CD

0

).

A2

D-71711A2

Part No.

0
0 Q)

CD CD

440SIT

N.A.

CD CD

@ Six

G)

Six

Q)

Six

(D Six

CD

Six

of
of

of
of
of

these

weights are included

these

weights

these

weights

these

weights are included

these

weights

are
are

are

included
included

included

in

Drive Clutch

in

Drive Clutch Elevation ,Kit (D-71712A

in

Drive Clutch Elevation

in

Drive Clutch Elevation

in

Drive Clutch Elevation

Modificat~on

Kit

(D-71711 A2).

Kit

(D-71712A2).

Kit

(D-71716A 1

Kit

(D-74124A

1).

).

1).

5NU•TWISTER

TIPSTER

HI-PERFORMANCE

(Flash 'Inside'

INTRODUCTION

It's

official!
season
sponsor
quick
months,
local drivers

The Sno-Twisters leaped
the final around the oval, all on Saturday. Then Sunday the crew came

honors

So, here's the bonus! We,

make the run
Sno-Twisters at Brandt's Lodge:

ENGINE

After

months

- on good old Alaskan snow ­of

the

kick-off

in

geography,

that

can

who

in

cross-country.

you'll

be real mean blizzard

had

"WIN"

for

the

Their Sno-Twister Customers)

of

spinning on hay

race meeting on

find

it

160 miles northeast

written

to

the

of

course, are happy

roses.

front

The

all over

following

Info

for

Mercury Snowmobile Dealers

and

straw,

has

opened

Nov

. .3rd and

territory.

their

and stayed there

with

4th

Ignoring all impending hazards, however, were

Sno-Twisters.

to

share

procedures were

11/16n3

or

a resounding

was Brandt's Lodge

of

Anchorage. Give or take a couple

to

win

the secrets

on

just

plain

grass,

"Margin

all three heats in

right

back

of

success

used

in setting-up the champion

NO.

to

Z-i-p

the snowmobile

for

Mercury".

...

and,

if

their

400

to

grab

so

that

you,

74-1

to

Eager

you're

class,
first

too,

real

of

plus

place

can

1. Check

2.

Adjust

engagement and

3. Check
The

spot-on
full
chocolate brown

timing

idle slow enough

for

following

for

racing. A Champion N55G plug

throttle

proper jetting.

jet

speed

BELOW 2000'

Temperature

Above

0.

Below

If

your

Mercury dealer doesn't
fails, a
340 jet.

Move
fourth

#53

drill

jet

needle

(4) notch

@3000 RPM

belt

sizes

run, the correct

color-

300

3QO

oo

(.059 dia.) corresponds

to

richer position

from

the

.100"

.±.

to

allow

drag, resulting in a slower start

will

serve

as

a guide, however, a proper plug check

must never appear whitish/grey.)

ELEVATION

Jet Size

290

to

320

to
to

330

have

jets,

by

top

of

the

jet

.005"

BTDC.

clutch

fuel/air

300
330
360

one notch; i.e. the retaining
needle.

to

reset. (Too high idle

off

is

easier

to

read

mixture

try

any dealer stocking

to a 320

will

jet, and a

the line.)

and

is

cause

2000'

Subtract 1 0

1/16

speed

suitable

plug electrode

to

Mikuni

drill

for

4000'

ELEVATION

from

the

carburetor parts.

(.0625 dia.) corresponds

clip

should be moved

is

the

racing.

jet

will

only

to

sizes

cause

(After

partial

way

to

100 yd.

have a light

I isted on left.

If

all

else

to

to

get

a

the

DRIVE

SHEAVE

1. Inspect clutch and lube per instructions in the Owners "Operation

(C-90.68019).

2. Check engagement
Use

an

3.

accurate tachometer

RPM

and adjust

to

check engagement

if

necessary.

(OVER)

speed.

(USSA

says

and

Maintenance

4000

RPM

Manual"

max.)

DRIVEN

SHEAVE

1. Check alignment per the manual.

2. Set spring preload

3. US!: A NEW

4.

Adjust

belt tension per the manual.

at 2 full

BELT.

cams.

FUEL

ICE STUDS and

SLIDER/TRACK

OIL

Use

a 20:1 fuel-oil

Mercury Formula 25 Mercury Formula

NOTE:

Carbide wear
and

an

Ice studs (D-68441) must be installed on the track. A good starting
on each side,
in the center band
washers

You

may prefer

effort

considerably.

You

CARBIDES

skegs

oversize washer

utilizing

to

space

ADJUSTMENT

mix.

Only

the

following

Castrol Synthetic High Performance Snowmobile Oil

may

want

to

clamp

(D-68440) must

used

above the ski

the holes in the track bars. One

of

the track

the studs

to

set the steering in the

See

up

your

to

"Operation

or

wire the fuel lines

be

installed

but

should be attached

the

3/8"

oils are known

at

for

racing. The ski holes may need

to

make the carbide

or

two

to

allowable.

low

effort

and

position, since the carbides increase the steering

Maintenance Manual".

to

be

satisfactory

50

the fuel pump.

fit

properly.

point

additional rows

the rubber

for

SNO-TWISTER:

Mercury Formula

to

be

is

to

install eleven studs

of

only,

eleven

not

thru

can

the bar.

500

drilled

be added

out

Use

The track must be adjusted
run smoother

is

load
track.

As outlined
that
position. Set yours

TETHER

Disconnect

engine.

Attach

must be pulled free before the tether is disconnected.

Check the tether switch operation. Moisture

malfunction. Gasoline de-icer

COWL

The aluminum hinge rivets should be replaced
should be removed

taken

for

SWITCH

a paper

best

if

the drive sprockets

out

through the wear plates inside the tunnel,

in

your

Owners Manual, handling (oversteer and understeer)

weight

on-off

transfer, the rear springs should be

up

and test

switch wire

clip

to

or

taped

for

proper tension

are

lubricated

prior

to

racing.

from

#3

stud

the tether switch cord

will

eliminate the moisture.

and

the screws secured

as

outlined in

with

of

terminal block,

and

hook

the

will

cause

with

large

with

your

Owners Manual. The track

grease

the points

silicone sealer.

so

set

clip

head

soft

(STP

be

sure

and the

to

prevent accidentally stopping the

on the

to

steel rivets

works well). Most

to

lubricate the

can

be

adjusted.

front

throttle

freeze, resulting in a switch

cable

or

bolts. The headlight

edge

springs

so

that

of

the side

We

in

the clip

of

found

the %

will

the

**IMPORTANT

NOTE:

U.S.S.A.
we cannot

has

ruled

that

use

the boggie wheel

kits

for

racing.

S

no-

Twister I

Hi-Performance

Tipster

No. 75-1 (6/1174)

Mercury Marine
"Sno-Twister

To

get
included
manufactured

MR. DEALER - Mercury Marine has

Registration Cards. We've

We've
snowmobiles
information

/ Hi-Performance

the

project

in

the

after

done

is

introducing

in

gear, the

"Snowmobile

Sept.

1,

1974.

another

Tipster",

following

Information"

FREE

aimed

"IMPORTANT"

IMPORTANT

added

this

in response

for

racing)

in "Sno-Twister/Hi.Performance

who

RACING0to

to

many

wish

to

receive,

Important

Sno-Twister/Hi-Performance

customer

primarily

envelope

made

requests

from
Tipster"

for

an

the

the

Info

about

benefit:

racing machines.

shipped

important

"Primary

from

factory,

bulletins

Owner

Tipster

with

change

Use" section

owners

owner

on

Snowmobile

mailing list directive will

racing.

Registration

Tipster

direct

all Mercury

(primarily use

to

direct

mailing

Snowmobile

of

the

mail

of

and

Mailing List

of

the

new

be

Snowmobiles

card.

their

latest

To

compile

that

1)

intended

the

factory.

We're sure

service.

Only

you

We'll

also

advise
should
the

This

time-saving tips.

be

properly

customer

"Tipster"

will

such a customer

you

fill

out

and

mark

that

every racing

can

get him

owners

checked

be

mailed

sheet

will

mailing list via

all registration cards, 2)

the

registration

on

the

in

their

"Operation

on

the

the

"Tipster"

be

used exclusively

owner

racing

new

card

accordingly

will

"Tipster"

and

machine's

bulletin.

to

direct

you

ascertain

want

to

take

list! If

Maintenance"

Registration Card

notify

owners

computer

from

and

3)

you

advantage

he

races,

manual

of

mailing,
the

promptly

of

check

high

performance

it

is ESSENTIAL

owner

this

that,
under

the
mail all cards

FREE.

RACINGD.

C-90-71050 (5174)

if racing

RACING 0

primary

direct

information

use

to

mail

is

intended,

so

it

that

and

IMPORTANT:

identical

an

mailing

The

service is

at

the

same

intended

time.

strictly

as

an

owner

benefit.

Dealers still will receive

Sno-

Twister I

Hi-Performance

Tipster

POSSESSION

Possession

the

driver ample time

competition.

of

INITIAL SETUP

After receiving a Sno-Twister,
even disassemble
components and

precision

that

• Pay special attention
secure trigger and

NOTICE:
order,
75-3
advise
Lac,

Sno-Twister/Hi-Performance

starting

with

you

desire

Marine

and

give

75-1.

previous
Publications

the

•·

and

Mercury

WI

54935.

1975 SNO-TWISTER- (340

a Sno-Twister well

to

it

completely

their

assemblies meet with your satisfaction.

a surgeon would use.

stator

in

advance

get acquainted with

you

may

to

familiarize yourself with

It

to

all

nut

to

crankcase.

If

the

first

first

copy

"Tipster"

Dept., P .0.

number

S(T-

of

want

"Tipsters"

that

the

the

to

are in numerical

you

receive is

issues (75-1

Box

you

received.

440

S(T)-

'74-'75 racing season can be a very big assist.

sled and

thoroughly check

brings results!

and

bolt torque specifications.

(example)

and

75-2) -

1108,

Fond

du

No. 75-2

(11

120174)

COMPETITION SETUP INFORMATION

to

properly break it

the

engine assembly and possibly

all

the

parts and

If

so, rebuild

Use

the

"loctite"

in

before entering

to

make certain

engine with

on

the

all bolts

It

gives

that

all

care and

that

• When assembling cylinders
no

with

gasket overhang. Make certain

to

cylinder.

• Check carburetor float levels and adjust high and low speed mixture screws

• Reinstall engine assembly, then check

tension, track tension and alignment and adjust

BREAK -IN PERIOD

IMPORTANT: During break-in period, a slightly rich high speed mixture adjustment

Use

a good premium gasoline and Mere Snowmobile

the

mixture for

for

short

durations only --avoid sustained full

throttle

setting. Check spark plugs often

first few hours

Become familiar with

characteristics. This

is

the

very important

feel

of

of

RACE PREPARATION (BASIC)

Cleaning and Inspection: After

the

Visually check

engine and chassis for worn
head gaskets, pistons, rings and cylinders for excess wear, cracks, chipped chrome, etc. Repair
components as necessary. Check piston

the

crankcase, make sure

that

the

torque

to

running (until piston rings have seated properly). Run

throttle

to

ensure

the

sled (clutch engagement, shifting, sound, etc) and its handling

for

later testing.

that

break-in period

or

that

the

transfer ports are lined

cylinder head

converter alignment, drive

specifications (refer

Oil

when mixing gas/oil. Make

dome

is

centered directly over

to

specifications.

belt

tension, drive chain

to

Owner's Manual).

operation and prolonged operation
engine

is

is

not

overheated.

completed, thoroughly clean the snowmobile.

up

is

advisable.

it

a slightly richer

at

high

at a constant

broken parts. Remove cylinder heads and inspect

or

fit

and ring clearances (end gap and side clearance).

correctly,

the

RPM

replace

Secure exhaust headers

to

cylinders, using safety wire

Check ignition timing (should

be

.100"

BTDC [21%0]

or

).

bearing

mount

type

"Loctite"

on

hex screws.

Check ski alignment (parallel, measuring
rod attaching hole closest

to

the

steering shaft.

front

and rear

Try

both

of

skis).

For

positions for

easier (slower) steering, use

your

preference.

the

tie

Check track and suspension: Track tension
lubrication), shock absorbers (dampening/leakage), idler wheels (wear and free bearing movement), slide
wear bars

parts as necessary.

Chaincase: Clean

Check brake assembly (cam, pin and pucks for wear)

and

chassis

and

rub

strips. Check all

inspect chain, sprockets, jackshaft and bearings.

RACE PREPARATION (FINAL)

Check electrical wiring: Disconnect emergency
terminal block (located behind dash). Be sure
secure and in good condition. Red wire from electronic pack
connects

Install a "race-proven" ignition safety
carburetion; re-check
Manual)
slides and adjust idle speed, making sure full
freely. Check all fuel lines
crimped.

to

to

coil

on

rewind side. Make certain

carburetor

suit

conditions (temperature

and

hoses.

and

alignment, suspension cross shafts (wear/bending -

nuts

and bolts for wear

"free

floating" and correctly adjusted.

stop

switch (red switch

that

ground wire from

that

CD

wiring connectors are coupled securely.

stop

switch (tether switch)

float levels. Adjust high speed mixture needles (as outlined

and

Be

positive

elevation)

throttle

that

that

operation

the

lines are secure

connects

will

and

proper

to

be

encountered. Synchronize

is

attained and

torque.

on

throttle

CD

mounting base

to

PTO side coil; white wire

suit rider. Check

on

fittings and

Repair

throttle

control)

not

or

replace

from

to

engine is

and

adjust

in

Owner's

throttle

cable moves

pinched

or

Check
system is mounted securely.

Drive sheave (clutch): disassemble
wear
are properly seated in movable face. Engagement
lowered
be sure
bind fiber

Driven sheave: Disassemble and clean. Check condition
necessary. Reassemble
required (approximately 2 ramps)
(8250

Torque converter alignment: Check
Inspect drive belt

about

Drive chain: Drain and refill chaincase
Check

exhaust

and/or

by

to

RPM)

condition

and

system: Inspect

binding. Check all moving

removing them. No

match alignment mark

bushing-

- refer

adjust chain tension

no

lubrication is necessary.

and

to

Owner's Manual.

for

wear, distortion,

of

belt,

replace

for

more

lightly lubricate shaft and wear plates. Adjust return spring preload as

it-

to

cracks, broken parts

and

clean. Check fiber bushings

parts

for wear and restricted movement. Make sure

RPM

than

four

(4) spacers are allowed. When reassembling drive sheave,

on

movable sheave with mark

to

attain maximum recommended

and

adjust alignment (parallel

burn

spots

and

cracking. Check drive

refer

to

Owner's Manual.

with

3 oz. (3.1 imp. oz.)

specifications.

and

missing coupler springs. Make certain

in

movable and fixed sheaves for

can

be

of

raised

on

torque

of

by

adding spacers

sheave cover

bracket wear plates. Replace if

RPM

and

offset

automatic transmission fluid (ATF).

and

take

at

wide open

distance between sheaves).

belt

tension. If

that

on

care

that

ramps

spring

not

throttle

in

doubt

or

to

Suspension adjustments: Understeer and oversteer can be varied
cross shaft. Rear shocks can

weight transfer requires a

soft

be

adjusted for firm

settin9

at

rear-

refer

or

soft

ride, depending upon rider preference. Best

to

Owner's Manual.

by

changing spring tension on

front

Track/slide suspension alignment: Align track

first

to

slides, then

to

chassis

tunnel.

NOTE: Because the front control arm always is

suspension mounting holes slightly

achieve

Traction devices: Three types
surfaces

Placement and pattern

rivet in the outside

Track lubrication: Lubrication
of

tunnel and between drive sprockets

Skis/carbide wear
Marine.

perfect alignment

and

conditions.

ends

skegs:

of

D-68441
D-71925

D-71926

are

strictly rider preference, depending upon rider style and racing surface. The

of

each

Carbide wear

D-68440-1
D-71334

the

of

track bar

of

and

slider

suspension

studs

are

can

the track

and

skegs

track.

in

compression,

it

may

be

necessary to rework the

adjust alignment with the suspension bolts loose in order to

inside

available

Mere Stud (22
Mere Scat Stud (22
Mere

be

removed,

can

be

beneficiial

(STP

are

a MUST

Carbide
Carbide

the

chassis

from

Mercury Marine

Pes.

Carbi•tle

lubri•cant works well.)

Stud (22

if

absolutely

by

for

stock racing and

Sk•eg

{Pair-

Sk•eg

(Pair -

tunnel.

Per

Package)

Pes.

Per

Pes.

necessary,

reducing drag between track

10"

Carbide Inserts)

6"

Carbide Inserts)

for

various types

Package)

Per

Package)

to

are

available

of

place a stud.

and

from

Mercury

racing

sides

or

Badly chipped, bent
carbide

Special application:

application; i.e., high elevation,

skegs

influence handling

Driver Sprockets {340

broken carbide

At

this

time, the following equipment

D-1393-5872A 1
D-1393-5854A 1
D-71712A1
D-71711A1

C-58601A1

(1) D-69757-12

D-68439
D-64684 14
D-63318A 1

D-64131

(1)

One C-23-69842 spacer

skegs

should

to

a high degree and, again,

cross

country

SIT

and 440 SIT)

12

Tooth

13 Tooth

Tooth

15

Tooth

16 Tooth

must

be

racing and modified racing:

High
High
High
Modified Drive
Bogie

used with 12

be

replaced immediately. Placement

are

mostly rider preference.

is

available

Eleva1tion
Eleva1tion
Eleva1

tion Drive

WheEl!

prive

(2)1

D-71483

(2)1

Kit -340

78

Carburetor
Carburetor

Sheave

Chain {340

pitch chain

from

Kit
Kit • 440

Sheave

Kit-

SIT and

Mercury Marine

- 340

Kit

- 340

340

SIT and

440

SIT

and

must

be

sprocket.

tooth

sprocket.

and

length

for

S/T
SIT

SIT

and

440

440

SIT

SIT

440

S/T)

78 pitch length

used with

16

of

special

S/T

tooth

CONCLUSION

The aforementioned steps
Sno-Twister
will--

produce a competitive Sno-Twister

for

competition. Hard

have

touched basically on major

work,

patience, thorouuhness

that

will

win

aspects

consistently.

of

setting

and

a strong desire

up

a 1975 Mercury

to

win can--

and

-

MERCURY MARINE - CERTIFIED SNOWMOBILE SPECIFICATIONS

M

ODEL

NAME

IN

E SPECIFICAT IONS

ENG

Engine Manufacturer
Engine

Model

No.

of

Cylinders

Engine Displacement

of

Cooling

Type
Bore 65.0
Stroke
Ignition
Min.

Compressed Head
Gasket Thickness
Min.

Compressed

Gasket Thickness

~~olume

<D

of

Spark Plug Hole
Crankcase Volume
Overall Length
Depth

-Top

to

Bottom

Depth·

Top

to

Top

of

Depth-

Top

to

Top

of

No.

of

Transfer Ports 4

Width

of
of

Width

Width

of

Height

of

Height

of

Weight-Piston Assembly
Complete

Overall Height
No.

of

Rings per Piston 1

Ring Type
Ring Thickness

Crankcase
of

Crar>kshaft

Main Bearing
Muffler

Make

DBA

Level 82+2

Head Pipe Length

Piston @

Base

Head

to

Top

of

Cylinder 109.0+0.01

of

Cylinder

of

Intake Port

of

Cylinder

Exhaust

Port

of

Cylinder

Transfer

Transfer Ports

Intake Ports 46.0
Exhaust Ports 40.0
Transfer Ports

Intake Ports 29.0

Face

Type

of

to

Port

Piston

Center

TDC

SNO-TWISTER

Kohler
K400-2RS
2

398.2
FA

60.0
CD

0.95

0.35

of

19.0

290.0

90.5

30.0

47.0

32.0/11.7

13.0

300gr.:!:,20gr

71.7

L-Ring

2.0

70.0

Sea

led-Ball

Mere/Donaldson

98.5

1974

NOTE:
Inches

Kohler Kohler Kohler Kohler
K340-2RS K440-2RS
2

339.3 429.4 435.8 338.1 437.9
FA

60.0 67.5 68.0 62.0 66.0

60.0 60.0 60.0 56.0 64.0
CD CD CD

1.2

0.3

14.7

305.0

109.0±.5

90.Q±1.5 95.3±1.5 92.0+.75/-1.0

29.5_±1.5 29.0_±1.5

46.25±1.5
4

33.0.:!:,1.5/

45.0+1.5 43.0+1.5 48.0+1.0 37.0+1.0

37.0;!:1.5 43.0±1.5 42.4+.75 37.0+.75 40.0+1.0

14.0+1.0

28.5+1.0 30.3+1.0 24.0+.5 22.5+.5
240gr;!:10gr

67.5+.55
1 1 2 2
Dykes Keystone Dykes Keystone

2.0+.08 2.5+.08 2.0+.08 2.0+.08

70.0±.5 70.0;!:.5 70.0±.2 58.0;!:.1 70.23±.2

Sealed-Ball
Mercury
82+2

117.0+2 167.6+2

All

length

(");A

ll

Volume Is in C

1975 1975

340

S/T

12.5±1.0

Measurements Are in Milli

ubic

Centimete

440S/T

2 2 2 2

FA

0,7

0.3

19.0

305.0

109.0+.5

46.25.:!:,1.5
4 4 2 4

33.0+1.5/

13.0

;!:

1.0 13.7+1.0

14.0+1.0 13.7+1.0 14.0

310gr

;t

10gr 335gr;t10% 240gr;!:10%

70.7+.5~

Sealed-Ball Sealed-Ball
Mercury Mercury
82+2 82+2 82+2 82+2

1975

440

K440-2RS K340-2AX KEC-440/22

Fa

n

1.1

0.3

21

.7 17.7

630.0+10% 463.0+10% 931.0+10%

109.0 + .1/-.2 98.3+.2

33.5+.4/-.6 34.43+ .4/-.6

47 .8+ .6/·1.2 43.8+ .6/-1

35.0+1.0/

71.7+.5 64.1+.5 71.42+.5

"L"

& Rectangular

"Y"-Manifold

meters

, unless

Spec

rs (Conversion Table Below).

TIT

1975

340 S/R 440 M/X

Fan

Mag

1.2

0.3 0.3

84.3+.75/-1.0

.2

27.0.:!:,1.0

:!:_1.

0 13.5+1.0

"L"

& R,ectangular Rectangular

Sea

led-Ball

ACS

24.5"+.25"

ifi

Kioritz

Fan

Mag

1.1

21.4_±5%

115.95+.5
Reed

37.5_±1.0

51.5.:!:,1.0

85.0_±2.0

Reed Valve

Reed
307gr±10%

2

1.5+0.1

Sea
Cowl

15.25"+.25"

led-Ball

ed

1975

Valve

Valve

1975 1975

440 S/R

Kioritz
KEC-440/22
2

437.9 644
Fan

66.0

64.0 65.07

Mag

1.1

0.3

21.4:!_5%

931.0+10%

115.95+.5 174.62
Reed

Valve

37.5_±1.0

51.5.:!:,1.0
4 2

85.0.:!:,2.0
Reed

Valve

40.0+1.0

13.5+1.0

Reed

Valve Reed Valve

307gr:!:_10%

71.42+.5 75.41
2 3

Rectangular Cast Iron

1.5+0.1 1.57

70.23;!:.2

Sealed-Ball

Cowl Mercury

82+2 82+2

15.25";!:.25" 127.0

Markll

Mercury
Markll

2

Fan

79.37

CD
N.A.

N.A.

28.5
N.A.

Boost • 53.08

39.11

50.80

35.05
Reed Valve

47.0

20.32

491.68gr

1-Piece

Sealed-Ball

~

~

I

~

.....

9

~

::r

-·

C3l

~

.!.'%

.,..

...

1

i

~

3

:a

g:

n

..

...

~

'tl

0~

:

!l

-·

:;·

;;;

g

3

-·

~·

~

~

~

~.

~

~

~

Q

~

~

~

!;'t~a~

!'

-·

w

:;16:-"c;

~~g:Sl~

~;:;

o.;t,g>

t:~~.g

....

C~-t

::l

3: ~ ...

0.

91

~-

i'

a·

Cl)

-o-a

g.

c ; .

co!!:<:;;~

:.

c:r

o·

~

~.:;;

::l g

-4:!:

3

"'

-·

O'tl

i

~

i g

...

,..

""'"0

g.~

~<

..

~

~-<

.. 0

<.

'"e'"

Og'tn-.~

c

-lll

~

)( ~ !2.

4\):::.:...~CD

[ 0

..

00::~"'

•

.,

0.

0

'-J:

&_1,113~

1\.)'tl

o.-&f.l

C

I--

~

~

~

.

~

I

~

~

"""'

i\;

~

...........

~

.........::

~

~

(I)

CARBURETOR

Make/Model No.

per

Engine

No.
Venturi -Smallest

Diameter in
Throttle

Downstream
Choke

DRI

VE CLUTCH

Make/Model No. Comet/100C XXXX-061
Engagement Speed
No.

Spring Wire Diameter

No.
Arm/Roller

DRIVEN CLUTCH

Make/Model No.
Spring Wire Diameter

No.
Ramp Angle

CHASSIS/SUSPENSION

Chassis

Suspension
Chassis
Ski Length
Ski Width 117+3.1 117 .6+1.5 117 .6+1.5 117.6+1.5

TRACK

Make Goodyear Goodyear Goodyear Goodyear Goodyear Goodyear Goodyear Mercury
Material

Width
Length ­Track Drive Sprocket Teeth

CHA

lNCASE

Standard Drive Sprocket
No.

Standard Driven Sprocket
No.

Optional Drive Sprockets
No.

Optional Driven Sprockets
No. of Teeth

Snowmobile Weight(Pounds

Throat

Bore - Largest Dia.

of

Butterfly

of

Springs/Color

of

Coils 4.8

Weight 38.6gr+.5gr 18gr+1.5gr 22gr+1.5gr 50.08gr+ .5gr 40.12gr+.5gr

of

Coils

Model

Length

0 .D.

of

Teeth

of

Teeth

of

Teeth

MikuniNM·36 Mikuni/36/34RS
2

36.0 36.0 36.0

37.0 36.12
Yes Yes Yes

3800-4000
1/Red 1/Biue 1 /Blue

4.75

Comet/90D Salsbury/152110

4.75
6 6.25
45°

66769 70729 70729 72006 66602/70238 68345 69869 66011
Slide Rail

1880+6.3 2235+6
1000±6.3 952.5+3 952.5+3 952.5+3 1008.4+3 1008.4+3 1008.4+3 993.78

Rubber/ Rubber/ Rubber/ Rubber/

Steel Bars Steel Bars Steel Bars Steel Bars

381+3.2 381.0+3/ -1.5 381.0+3/-1.5

2820 2816.4+12.5 2816.4+12.5 2816.4+12.5

2 2

Arctic

Cat/

RPM

2)

4000RPM Max.

92"

.1

3.9 3.9

.192" .192"

41° 41°

Slide Rail

9 9

15
34 34 34 34

13-14-16 12-13-15-16-17 12-13-14-16-17

.A.

N
360+10 365

14

N.A. N

Mikuni/36/44RS

36.12 36.1

Arctic

Cat/

XXXX-062

2)4000

RPM

.192"

Salsbury/152110 Salsbury/850 Salsbury/850 Salsbury/850 Mercury Salsbury

6.25 6.25+.2

Slide Rail Slide Rail Slide Rail
2235+6

9

15 17 15

.A.

365 365 350 390 380 500

MikuniNM
2 1 1 1

36.0 39.7

Yes

Salsbury/850

Max. 3300 RPM+10% 3500 RPM+10% 3500 RPM+10% 3400 RPM+10%

1/Piain

4.32 4.32

5.4+.2 5.4+.2 5.4+.2

4.88 3.96 3.

350

2235+6

381.0+3/-1.5 387.35

9

12-13·14-15-16-18 12-13-14-16·17
28-36·38-40

·36 Walbro/WDA·50

41.3
Yes

Salsbury/850 Salsbury

1/Piain

5+.2 5+.2 6+.2

320

+6

2209.8

136.6+1.5 136.6+1.5 136.6+1.5

Rubber/Grouser Rubber

3072.4

8

36 36 28

28-34·38-40 28-34-38-40

Walbro/WDA-47 Walbro/WDA-47 Walbro/WRA-3

2

39.7

41.3
Yes Yes Yes

/850

1/Piain 1/Piain 1/Piain

4.32 4.74 4.3

43.86gr+.5gr 65.32gr+.5gr 51.32gr+.5gr

96

32°

Bogie Wheel Slide Rail Swing Frame
2247+6

387.35 387.35 431.8

3009.9

39.7

41.3 38.1

Mercury Salsbury/850

5.2+.2

5.71

40°

2247+6

Rubber/Grouser Rubber

3072.4 3327.4

32.5

3200 RPM+10%

5.4±.2

4.3
7+.2
32°

2521

152.4

8 8 8

17

12-13-14-15-16-18 12-13-14-15·16·17

-18

18

34-36·38·40 28-34·38·40

16
36

12·13·14-15·17 ·18

/850

NA. a Not

Applicable

METRIC CONVERSION: 1mm (millimeter) =

cc

(cubic centimeter) = 0.06 cu.in.; 1 1

1

0.0394"

(inch); 1 gr (gram) = 0.04 oz.;

b.

(pound) = 0.4536kg (kilogram)

(D

0-4 Spacers (.06 Thick)

to

Achieve 4000 RPM Max.

Sno-

Twister I

Hi-Performan

ce

Tipster

NOTICE: $no-Twister/Hi-Performance

order,

starting

with

75-3 ••

and

advise Mercury Marine Publications

lac,

WI

54935,

75-1.

you

desire previous

and

give

Driven

We

have received a few reports

in

crack (as shown

Figure

Thus far, complete breakage has
At

this time, and only

support

brace (as shown in Figure

as

that

1)

because

not

occurred.

a temporary measure,

2)

to

A new, stronger pillow block with a

If

the

the

first

Shaft

the

driven shaft pillow block (D-71007) has developed a small

of

the

reinforce
support

"Tipsters"

first

copy

"Tipster"

number

Dept.,

issues (75-1
P.O.

that

Pillow Block -

torque

we

the

brace

no-charge replacement. As soon as parts are available,

are in numerical

you

receive

is

(example)

and

1108,

1975

75-2)-

Fond

340

du

S(T,

to

No

440

which

. 75-4

SfT

and

the

block

(11

122/74)

440

is

subjected.

Box

you

received.

load and stress

recommend construction and installation
block.

is

in

process and will be available soon for

details

will follow

in

a later bulletin.

T

fT

of

Models

a

Figure

Support

Brace
Installed

2.

Sup

: Al

•

port

Brace

uminum

Figure
Cracked
Pillow
Block

14" Long

l"Wide

lja"Thick

1.

09009

Sno-

Twister I

Hi-Performance

Tipster

It's official - On

the
Snowmobiles kicked
nand

Stock m classes. Here are some set-up

NOTICE: Sno-Twister/Hi-Performance
order, starting

75-3 --and

advise Mercury Marine Publications
Lac,

WI

weekend

off

with

75-1.

If

you

desire previous

54935. and

give

of

the

1974-75 snowmobile racing season with resounding victories in Stock

the

the

first

November

"Tipsters"

first

copy

"Tipster"

Dept.,

number

2nd

tips

that

are in numerical

you

receive is (example)

issues (75-1

P.O.

that

you

Box

received.

and

1108,

& 3rd, 1974,

helped pull

75-2) -

Fond

du

1974-75

in

Alaska, Mercury Sno-Twister

it

off.

No. 75-5

"Race

Proven" Set-Up Tips

(11

IMPORTANT: These set-up tips and specifications are intended for use under race conditions

ONLY!

ENGINE

1. Check ignition timing (.100"

2. Make sure

3.

Idle

Set

and

CARBURETION

that

idle

RPM

is

set

RPM

too

high causes belt drag, resulting in a slower start

the

low speed mixture needles (air

±

.005"

low enough

BTDC

pilot

at

3000

RPM).

to

permit drive clutch

screws)

on

both

off

the

to

reset (disengage from belt).

the

line.

340

Sff

and

440

Sff

at
open from seat.
Set

4.

carburetor

340

440

5.

Use

the
determine approximate setting
determine final setting by "reading" spark plug color

(refer

to

jet

needles as follows:

S{f-

"E"

ring

S/T-

"E"

ring in 1st (top notch).

chart

and graph in

Owners Manual

in

2nd notch from

the

Owners "Operation and Maintenance" Manual as a guide

of

for

procedure) .

top.

high speed mixture needles. However, POSITIVELY

after

making a few

100

yd. WOT runs

/22/74}

2 turns

to

TORQUE CONVERTER

1.

Set

driven sheave spring preload

at

WOT and readjust if necessary.

NOTE:

achieve a uslip
helps.

2.

Clean and inspect drive clutch as outlined in Owners Manual.

To assist future adjustments

fit"

on the steel shaft

at

2 full cams [30-32 lbs. (13.6-14.5kg)] . Check for

and/or

of

repairs, remove burrs from torque bracket

the

fixed

sheave. A light

3. Check and adjust drive belt tension as outlined in Owners Manual.
RPM

4. Check clutch engagement

and adjust if necessary.

IMPORTANT: Use a dependable and accurate service tachometer

on

your

strictly

snowmobile tachometer. (USSA rules specify 4000

ment.)

film

of

grease

to

check RPM.

RPM

8250

RPM

ID

to

on

the shaft also

Don't

rely

maximum engage-

TRACK/SUSPENSION

1. Adjust track tension and alignment as outlined in Owners Manual.

2.

Lubricate drive sprockets and

both

edges

of

track

for

smoother running with less drag (STP

works well).

3.

For

best results

front

suspension springs as test results

4. Check tightness
pivot (saddle)

of

weight transfer, set spring preload on rear shocks soft and set tension

on

a particular track may dictate.

of

all fasteners regularly before each race, particularly

to

the

leaf spring assembly and bolts which secure

TETHER SWITCH

Type

of

Obtain and install a "race proven" Safety Tether Switch.

IS

strictly driver preference. (Safety Tether Switch

To

IMPORTANT:

disconnecting

the

wire from No. 1 position

prevent accidentally stopping

emergency

stop

switch (red), located

on

terminal block.)

NOT available from Mercury Marine.)

the

on

switch and mounting location are

engine during a race, we suggest

the

throttle control. (Remove orange

TRACTION DEVICES

the

ski assembly

bolts

that

secure

to

the

on

the

ski

spindle.

1. Carbide insert wear skeg (Mercury Marine
racing.

2.

The
pack"

NOTE:

following

and ice.

Patterns shown are viewed

"stud"

patterns are typical

from

the

bottom

Part

No. D-68440-1)

of

installations

of

the track, rear

on

the

skis are a MUST

that

performed very well on

to

front.

for

"hard

KEY

440

S/T

X = Mere Carbide Stud (Part No. D-71926-

Stud

Z = Mere Scat

Scat Stud o

5th

every

bar-

LEFT

side only

(11

pes.

required)

n

(Part No.

ll•z•

llx

•

•

II·

llx

•

I

D-71925-

FRONT

A

I'

I 1 If' I

+

I
I
I

I
I

+

I
I
I
I
I

+

I
I

I

I

I

+

I

I

I

I I

I

I

-r-

I
I
I
I
I

+

I

z

I

!

I

:

I

I

I

I

!

I

-,-

I
I

I

I

22

/1

22

pes.

•

•

•

•

pes.

in pkg.) (Super Stud)

in

pkg.) (Kangaroo-

Carbide Stud on every bar, alternating from side

t

xll

·II

o side (44 pes. required).

Scat Stud with spacer underneath

(

9.5mm) maximum height allowed. Attach
rack (not on bar) alternately (after every

t

t

rack bar)

shown

xll

........

Track Bar

""

~

Rivet

"

1%"

on

centerlines

(11

pes. required).

x

%"-

5/8"

bite)

to

achieve 3/

of

track drive lugs, as

8"

to

4th

ll•z•

llx

•

II·

•

llx

•

ll•z•

llx

•

•

II·

J

~~

+ +

I

I

I
I

I I

I

:

...

I

+ +

I I

z

I

I I

-1--

I

I

I I
I
I

I

-1--

I

I

I
I

I
I

..L

I I

;

I

I
I

I

-L

I

i

I

I

I

I

J_

I

-y

I
I

I

_L

I

i

I
I
I

..L

I
I

I

I

l

-L

1

I

I

I

I

-l-

i

1

z

l

I

-r-

I I

REAR

•

•

•

•

•

•

•

1--

~~

xll

-

·11

xll

·II

xll

·II

xJI

Drive Lug Centerline

Type 1 - Stud Mount: Standard (original equip­ment) mounting. Torque

DO

(1.1-1.4mkg).

bolt flush with track fabric.
Type 2 - Alternate Mount:

bolt, a %"
head and standard locknut. Torque

NOTE: Drawing the
deeply
premature loosening

track fabric .

ID

into

Type 1

NOT

washer with a large

the track usually

of

(Optional Spacer)

to 8-10

attempt

Use

bolt

head

stud

and/or

Type2

to

%-28

OD

to

will

ft. lbs.

draw head

pan head

under

8-10ft. lbs.

or

washer

result in

tearing

of

bolt

of

KEY
X=

Mere Carbide Stud (Part No. D-71926-

=Mere

Z

Scat

llx

II·

llx

II·

llx

II·

llx

II·

fix

lr·

llx

Stud

(Part No.

FRONT

..;,

I

I'J

I I

•

•

•

•

•

+

I

I
I
I

I

+

I
I

I

I
I

+

I
I

I
I
I

+

I
I
I
I
I

+

I

z I

I

I

• +

I I

I

I

•

•

•

•

•

•

•

-'-

I I

i

•

I
I

I

_L

I I

-.

I
I
I
I

..L

I

;

I
I
I

I

~

I I
I

I

I
I
I

..J_

I

.....

I

I

-y

D-71925-

d

I~'

I

~

I
I

z

I

+

I
I
I
I

!

I

-:

I

I
I

•

!

--:

'

I

I

I

I

!

+

I

I

•

+

I

•

I
I

-1-

I
I

I
I

I

..L

1

I

•

I

-L

T

;

z

i

I

-L

;

•

I

•

~

i

I I

REAR

340

I

•

•

•

•

•

•

•

•

•

•

•

I -

-f'

5/T

22

22

pes.

·JI

xlf

·If

I'

"

xll

I

-1

xtl

·II

xll

·II

xlJ

·II

pes.

in pkg.) (Super Stud)

in

pkg.) (Kangaroo-

Carbide Stud on every bar, alternating from side
to

side (44 pes. required).

Scat Stud with spacer underneath
(9.5mm) maximum height allowed. Attach
track (not on bar) alternately (after every
track bar) on centerlines of track drive lugs, as
shown

Track

Rivet

Drive Lug Centerline

Type 1 ­ment) mounting. Torque
(1'.1-1.4mkg).
bolt flush with track fabric.

Tupe 2 - Alternate Mount:
bolt, a %" I D washer with a large

head and standard locknut. Torque

(11

pes. required).

Bar

Stud

Mount: Standard (original equip-

DO

NOTE: Drawing the

into

deeply
premature loosening

track fabric.

the track usually

Type 1 Type 2

1%"

NOT

attempt

bolt

of

stud

(Optional

x

%"-

to

Use

head

and/or

Spacer)

5/8"

bite)

to

achieve

8-10 ft. lbs .

to

draw head of

%-28 pan head

00

to

8-lO

or

will

result in

tearing

3/8"

under bolt

ft.

washer

of

to

4th

lbs.

Sno-

Twister I

Hi-Performan

e Tipster

NOTICE: Sno-Twister/Hi.Performance
order, starting with 75-1.

75-3

--

and

you
advise Mercury Marine Publications
Lac,

WI

54935_

340

IMPORTANT: Modification

Modification instructions

CAUTION: Modify engine, exhaust system and carlt>uretion EXACTLY
following. ANY DEVIATION from SPECIFIED DIMIENSIONS
PARTS NOT MENTIONED WILL DECREASE PERFORMANCE and could result in severe
engine damage.

S/T

Modifying 340

desire previous

and

MODIFICATION INSTRUCTIONS

are

S/T

If

the

give

the

first

of

exhaust

intended solely for race applications.

from

"Tipsters"

first

copy

"Tipster"

Dept., P .0.

number

system

that

are in numerical

you

receive

issues (75-1

Box

1108,

you

receiAied.

and/or

is

(example)

and

75-2) -

Fond

du

No.

75-6

(11

engine VOIDS your WARRANTY.

as

instructed,

or

MODIFICATION

"Stock" to "Modified-Stock"

CYLINDER

A. Exhaust Port

port

of

Enlarge exhaust

1. Raise

2.

top

edge
(Figure 1) DO NOT change
Increase

the

chordal

cylinder as follows:

of

exhaust

width

port

bottom

of

exhaust

to a point

edge

of

port

to

1.120" (28.45mm) below

exhaust port:.

1.460"

{3:7.08mm). (Figure

top

1)

surface

122174)

of

of

cylinder.

NOTE:
following

3.

Enlarge radius

4.

After

Chordal

curvature

grinding exhaust

IN

width

of

of

4 exhaust

Raise Exhaust

below

Top

Surface

Enlarge Radius
Bottom Inlet Port

Corners

Increase Chordal Width

Exhaust Port

(Figure 1) is straight

cylinder

port,

Port

to~"

wall).

port

corners

chamfer all sharp edges.

to

1.120"

of

Cylinder

of

2

of

to

1.460"

to.Q...2Q:

line

distance between side

(5.1mm). {Figure 1)

Lower llnlet Port

below

To1p

Surface

to

of

edges

3.675"
Cylinder

Enlarge Radius

Port

C«(

-

~

; I 1

. .

. .

' !

of

port

(not

of

4 Exhaust

·

:

·

r--0·]

EX

Figure 1.

340

IN

--------

S/T

"Modified-Stock" and "Super-Mo1dified" Cylinder Dimensions

Shape
Shape

of

"Stock"

of

Modified Ports

Ports

B.

Inlet

Port

port

of

Enlarge inlet

1.

Lower
(Figure 1) DO

2. Enlarge radius
After

3.

bottom

grinding inlet

cylinder

edge

of

NOT

change

of 2 bottom

port,

EXHAUST SYSTEM

Modification

of

"stock"

exhaust system

CARBURETION

Adjust high

"normal"

speed

coloration

mixtures (adjust mixture needles and/or replace fixed high

of

spark plugs.

as

follows:

inlet

port

to a point

top

edge

or

inlet

port

corners

chamfer all sharp

is

chordal

edges.

not

permitted

3.675"
width

to

0.25"

(93.35mm) below

of

iniHt

port.

(6.35mm). (Figure 1)

for

"modified-stock"

top

surface

competition.

speed

of

jets)

cylinder.

to

attain

CAUTION:
"richer"
engine

When

setting. Carburetors, which

damage.

in

doubt

about high

are

speed

adjusted

DRIVE SYSTEM

A. Maximum Engine

A

"modified-stock"

Modify

B. Drive

Install Drive

correct

and

adjust torque converter

Sheave

Sheave

full

throttle

NOTE: Clutch modification instructions are supplied

C.

Sprockets

Snowmobile may require "re-gearing"
modification). Installation

to

conditions)
Chart", following.)

change

RPM

340 SIT

(Clutch)

Modification

engine

top

will

deliver maximum power when operated

to

increase full

Kit

(D-71711A 1 ).

RPM

(as

recommended in preceding

because

of

another driver sprocket may be desired (depending upon operating

speed

of

snowmobile (MPH)

mixture

too

throttle

Modify

with

of

increase1d

and

adjustment,

"loan",

engine

profile

!Paragraph)

will

RPM

of

ALWAYS

cause

at

to

this

drive

sheave

and desired

modification kit.

horsepower

accetleration. (Refer

severe

8,750

speed.

(a

result

to

"Driver

select a

internal

to

9,000

ramps

shift

RPM

to

attain

pattern.

of

engine

Sprocket

.

DRIVER

Top

Speed

of

Snowmobile (MPH) No.

MPH

High

MPH

Low

• Standard (factory installed)

SPROCKET CHAFtT

of

17 D-63573
16 D-64131
15

14•

13 D-68439
12 D-69757-12

340

SIT

driver sprocket

Tee1th

Part Number

D-63318A1
D-64684

Modifying 340 S/T

ENGINE

A. Cylinder

from

"Stock"

to

"Super-Modified"

1. Exhaust Port - Enlarge cylinder exhaust

to

'Modified-Stock'~

2. Inlet Port - Enlarge cylinder inlet

'Modified-Stock''~

B. Ignition Timing

Retard ignition timing

preceding.

preceding.

{full

advance) from

port

as outlined

port

as outlined in "Modifying

0.100"

BTDC

to

0.080"

in

"Modifying

BTDC

340

340

SIT

{2.54mm

SIT

from

to

EXHAUST SYSTEM

A. Exhaust Pipe Center Section

1.

Cut~

2. Before re-welding exhaust pipes, position pipes in snowmobile and rotate sections
fit.

3.

Weld sections
exhaust.

B.

Exhaust Pipe Stinger

1.

Cut production stinger from each exhaust pipe.

NOTE: Converging cone

diameter (!D)

{11.43cm) from center section

of

exhaust pipes together.

of

exhaust pipes may

of

cones

are enlarged to

J::.

of

each exhaust pipe. {Figure 2)

Be

sure

that

welds are smooth and

have

(25.4mm)

to be

(same

cut

ID

as

replacement stinger).

do

back slightly,

from

'Stock'

'Stock'

2.03mm).

to

attain best

not

restrict

so

that

to

inside

2. Weld modified stingers

1.02mm x 26.67cm) - Figure 2]

restrict exhaust.

~------\

/_

L

...£C_

'\,

~\0)

:.-:--

Modified
Stingers

-------.....J

[1"

ID x 0.040"

to

converging cones.

eon,

..

g;ng Cones

(Rotate fo• Ben

Sections)

thick {approximately) x 10.

Be

sure

that

welds are smooth and do not

Left

Pipe

5"

long {25.4mm x

Figure 2.

340

SIT "Super-Modified" Exhaust Pipes

CARBURETION

Adjust high speed mixtures (adjust mixture needles

"normal"

coloration

of

spark plugs.

and/or

replace fixed high speed jets)

to

achieve

CAUTION:
"richer"
engine damage.

When

setting. Carburetors, which are adjusted

in

doubt

about

high speed mixture adjustment, ALWAYS select a

DRIVE SYSTEM

A. Maximum Engine

A "super-modified"
Modify and adjust torque converter

B.

Drive Sheave (Clutch)

Install Drive Sheave Modification Kit (D-71711A 1

correct full

NOTE: Clutch modification instructions are supplied

C. Sprockets

Snowmobile may require "re-gearing" because
exhaust modification). Installation
operating conditions)
Sprocket

throttle

Chart", preceding.)

RPM

340

S!T will deliver maximum power when operated

to

increase full

engine

to

change

RPM

(as recommended in preceding paragraph) and desired

of

another driver sprocket may be desired (depending upon

top

speed

of

snowmobile

too

"lean",

throttle

).

of

increased horsepower

engine

Modify profile

with

(MPH)

RPM

modification kit.

and acceleration. (Refer

will cause severe internal

at

9,750

to

this speed.

of

drive sheave ramps

(a

result

to

10,000 RPM.

to

shift

pattern.

of

engine and

to

"Driver

attain

Sno-Twister/Hi-Performa ce Tipster

NOTICE: Sno-Twister/Hi-Perlormance

order, starting
75-3 --and
advise Mercury Marine Publications

Lac,

WI

440

S/T

IMPORTANT: Modification

with

75-1.

If

the

the

first

you

54935.

desire previous "

and

give

MODIFICATION I"ISTRUCTIONS

of

exhaust system

Modification instructions are intended solely

first

copy

Tipster"

Dept

number

"Tipsters"

you

recei~'e

issues (75-1

., P.O.

Box

that

you

for

aro in numerical

is

(example)

and

75-2)

-

11

108,

Fond

received.

and/or

du

engine VOIDS

race applications.

NO.

75-7

your

CAUTION: Modify engine, exhaust system and carburetion EXACTLY as instructed,

or

following. ANY DEVIATION from SPECIFIED DIMENSIONS

PARTS NOT MENTIONED

WILL

DECREASE

PEFUFORMANCE

MODIFICATION

and could result in

severe engine damage.

Modifying 440 S/T

from

"Stock" to "Modified-Stock"

ENGINE

A. Cylinder

1. Exhaust
a. Raise

b. Increase chordal width

Port-

top

(Figure 1)

Enlarge cylinder exhaust

edge

of

DO

NOT change

exhaust

port

of

exhaust

to a point

bottom

port

edge

port

as follows:

1.120"

of

exhaust

to

1.690"

(28.45mm) below

top

!POrt.

(42.93mm). (Figure 1)

surface

{11

122174}

WARRANTY.

of

of

cylinder.

NOTE: Chordal width (Figure

of

following curvature

c. Enlarge radius
d.

After grinding exhaust port, chamfer all sharp edges.

Enlarge Radius

of2

Top

Port

Inlet
Corners

0.20"~---

to

IN

cylinder wall).

of

4 exhaust

Raise Exhaust Port

to

1.120"

Surface

of

~~~IJmt~lr1r~f£~~,

"'"7

Enlarge Radius

2 Bottom Inlet Port

1)

port

below Top

Cylinder

of

is straight line distance between

corners

to 0.20"

Lower Inlet

Top Surface

~----

Increase Chordal Width
Inlet Port

(5

..

08mm).

Port

to

t[)f

Cylinder

Raise

Top

t1o

1.no"

side

edges

of

port

(not

(Figure 1)

3.850"

below

Inlet Port

to

2.470"

below

Surf~eofCylinder

EX

Enlarge Radius
Port Comers

of

to

of

0.20"

4 Exhaust

Increase Chordal Width
Exhaust Port

Figure

to

1.690"

1.

440

of

-------

----

Shape
Shape

of

"Stock"

of

Modified Ports

SIT "Modified-Stock" and "Super-Modified" Cylinder Dimensions

Ports

Page

2 Snowmobile "Tipster" No. 75·7

2. Inlet

Port-

a. Lower

Enlarge cylinder inlet

bottom

edge

of

inlet

port

port

cylinder. (Figure 1)

top

edge

of

inlet

port

b. Raise

to a point

(Figure 1)

of

inlet

c. Increase chordal width
d. Enlarge radius

corners

to

e. Enlarge radius

to 0.20"

(5.08mm). (Figure 1)

of 2 bottom

0.75"

(19.05mm). (Figure 1)

of 2 top

inlet

port

inlet

port

f. After grinding inlet port, chamfer all

sharp edges.

B.

Piston

as follows:

to a point 3.850"

2.470"

to

1.770" (44.

(62.

96mm)

port

corners

(97.79mm) below

74mm)

below

. (Figure

top

1)

top

surface

surface

of

cylinder.

of

IN

Remove
from Inlet Side
of

0.080"

Piston Skirt

Remove

0.080" (2.03mm) from inlet side

of
piston skirt. (Figure 2) After cutting piston skirt,
remove

all

NOTE:
exhaust

sharp edges from skirt.

Inlet

side

of

piston is side opposite

mark

on

piston

dome.

EXHAUST SYSTEM

Modification

of

"stock"

exhaust system

is

not

permitted for "modified-stock" competition.

CARBURETION

Adjust high speed mixtures (adjust mixture needles
"normal"

CAUTION: When in
"richer"

coloration

of

spark plugs.

doubt

about

high speed mixture adjustment, ALWAYS select a

setting. Carburetors, which are adjusted

engine damage.

DRIVE SYSTEM

A. Maximum Engine

RPM

----·--Shape

---

Figure 2.

and/or

rep,lace fixed high speed jets)

too

"lean",

of

"Stock"

Shape

440

of

Modified

SIT "Modified-stock" and

Piston f

Piston

"Super-Modified" Piston

will cause severe internal

to

+

obtain

A "modified-stock"
Modify and adjust

440

SIT will deliver maximum power

torque

converter

to

increase full

B. Drive Sheave (Clutch)

Install Drive Sheave Modification Kit (D-71711A 1

correct full

NOTE:

throttle

Clutch

engine

modification

RPM

(as recommended in preceding paragraph) and desired shift pattern.

instructions are supplied with

C. Sprockets

Snowmobile may require "re-gearing" because

of

modification). Installation

to

conditions)
Chart",

following.)

change

top

another

speed

of

driver sprocket may be desired (depending upon operating

snowmobile (MPH) and acceleration. {Refer

whe!n

operated

throttle

).

Modify profile

of

en1gine

modification

increased horsepower

at

8,500

RPM

to

this speed.

of

drive sheave ramps

kit.

{a

result

to

"Driver Sprocket

to

8,750

to

of

engine

RPM.

attain

Page 3 Snowmobile

Top

Speed

"Tipster"

of

High

Low

No.

75·7

DRIVER SPROCKET CHART

Snowmobile (MPH)

MPH

MPH

Number

of

Teeth Part Number

17

16

15.
14
13
12

D-63573
D-64131
D-63318A1
D-64684
D-68439
D-69757-12

• Standard (factory installed)

Modifying 440

S/T

ENGINE

A.

Cylinder

1.

Exhaust Port -Enlarge cylinder exhaust

'Stock'

2.

Inlet

'Stock'

B.

Piston

Modify
preceding.

to

'Modified-Stock'

Port - Enlarge cylinder

to

'Modified-Stock'

piston {Figure

2)

as

",

preceding.

",

preceding.

outlined in

from

inlet

port

440

SIT

driver sprocket

"Stock"

port

{Figure

(Figure

"Modifying

1)

440

1)

as

to

"Super-Modified"

as

outlined in

outlined in

SIT

from 'Stock'

"Modifying

"Modifying

to

'Modified-Stock'

440

SIT

from

440 SIT from

",

"Squish"

Figure

C.

Cylinder Head

1. Machine

2. Re-cut cylinder
{Figure

3. Remove all

4. Volume

D. Ignition Timing

Retard ignition timing

Area

3.

440

0.065"

3)
sharp

of

modified cylinder

Re-Cut

Area

~,

Diameter)

SIT

{1.65mm) from

head

edges

(full

"Squish"

out

to

(Original

"Super-Modified" Cylinder Head

"squish"

from

edge

head

advance) from

face

area

at

of

{measured

----­___

of

cylinder head. {Figure 3)

20°

"squish"

0.100"

Shape

Cylinder Head

Shape

Cylinder Head

and

out

area.

on

flat

(2.54mm) BTDC

of
of

to

original diameter

{Figure

plate) should

"Stock"

Modified

3)
be

to

0.080"

CcttEae~r

Header

fo.l:Q:,

Figure

440 SIT "Super-

Modified"

Header Pipe

[2.657"

23.8cc.

{2.03mm) BTDC.

J

PiPe

4.

Exhaust

{64.49mm)].

Page

4 Snowmobile "Tipster" No. 75·7

EXHAUST SYSTEM

A.

Exhaust Header Pipe

Cut each header pipe down

to

2.0"

(50.8mm) including flange. (Figure 4)

NOTE:

B.

Exhaust Pipe Center Section

1.

Cut 1.0" (25.4mm) from center section

2.

Before re-welding exhaust pipes, position pipes

Re-weld spring attaching

washers

fit.

NOTE: Spring hooks

tension.
engine rewind housing. Bend
Figure 5).

3.

Weld

Left

sections

exhaust pipe (PTO side)

of

will

require repositioning

left

exhaust

exhaust pipes together.

exhaust.

to

flange

of

each exhaust pipe. (Figure 5)

must

pipe

Be

of

header pipes.

in

snowmobile and rotate sections

on

exhaust pipes to give sufficient spring

be heated and

in area

sure

that

CAREFULLY

of

first bend (just

welds are smooth and do

Bend

Pipe in This Area

(Bend as

Fit

Left

around

bent

after

Exhaust

Required

Engine)

to

obtain best

to

fit

header

not

to

around

pipe

restrict

-

~-----\

/_

LV\-~·

-...\

CUt

Converging Cones Back Approximately

(ID

of

Cones MUST

C.

Exhaust Pipe Stingers

1.

Cut production stinger from each exhaust pipe.

2. Cut approximately
of

cones is enlarged

3. Weld modified stingers [1-1/8"

1.02mm x 38.1cm) - Figure 5]
restrict exhaust.

\D

Be

Same as ID

Figure

W'

to

eon

..

.,..

••

Cones

(Rotate
Fit

and

Center

for

Best

in

Snowmobile--------_,...

Re-Weld

5.

at

Sections)

Y.z"

of

Stingers)

440 SIT "Super-Modified" Exhaust Pipes

(12.7mm) from end

1-1/8" (28.58mm) (same I D as replacement stinger). (Figure 5)

ID x 0.040"

to

converging cones.

and

Weld

of

each converging cone so

thick (approximately) x

Be

sure

that

inside diameter (I

15"

long (28.58mm x

that

welds are smooth and

do

D)

not

Page

5 Snowmobile

CARBURETION

A.

Carburetors

"Tipster"

No.

75·7

Replace

are

B. High

1. Fixed high

2. Adjust high

"stock"

carburetors (Mikuni

available thru Mercury Marine

Speed

operation)
Mercury Marine

attain

CAUTION:

"richer"

Mixture

speed

will

"normal"

jets

be required in

(see

"Ordering

speed

mixtures (adjust

coloration

When

in

setting. Carburetors, which

engine damage.

C.

Ordering

To

obtain ordering

(No.

400

Information

information

to

No. 480), contact:

in

the

of

doubt

VM

36)

with

(see

"Ordering

range

of

No.

VM

38 carburetors. Fixed high

Information",

mixture

spark plugs.

about

on

high speed

are

adjusted

modified carburetors

Mercury Marine
Hi-Performance Products Department

20

Wisconsin Street

Oshkosh, Wisconsin 54901

Mikuni

Information",

400

to

VM

No.

38

carburetors (38mm). Carburetors

following).

480

(depending upon conditions

speed

jets

are

following).

needles and/or replace fixed high

mixture

too

adjustment,

"lean",

(Mikuni

ALWAYS

will

cause

VM

38) and fixed high

severe

available

speed

jets)

select a

internal

speed

of

thru

to

jets

DRIVE SYSTEM

A.

Maximum Engine RPM

A "super-modified" 440 SIT
Modify

B. Drive

Install Drive

correct

C.

and adjust torque converter

Sheave

full

NOTE:

(Clutch)

Sheave

throttle

Modification

engine

Clutch modification instructions are supplied

Sprockets

Snowmobile may require "re-gearing"
exhaust modification). Installation
operating conditions)
Sprocket

Chart",

to

preceding.)

will

RPM

change

deliver maximum power when operated

to

Kit

(as

recommended

of

top

speed

Attention:

Snowmobile Division

Telephone: [phone]

increase

(D-71711 A 1 ).

because

full

throttle

Modify

in

preceding paragraph) and desired

of

increased horsepower

engine

profile

with

modification kit.

another driver sprocket

of

snowmobile (MPH) and acceleration. (Refer

at

RPM

of

to

this

drive

9,500

sheave

to

speed.

ramps

shift

(a

result

may

be desired (depending upon

of

9,750 RPM.

to

obtain

pattern.

engine and

to

"Driver

•

)

)

Sno

-Twister

/Hi-Performance

Tipster

NOTICE:
order,

75-3 --and

advise Mercury
Lac.

starting

WI

54935,

Sno-

Twister/Hi-Performance
with

75-1.

you

desire previous

Marine
and

If

Publications

give

the

first

the

first
"Tipster"

number

TRACK "STUD" INSTALLATION

1975 Models 340

S/T,

(Chassis Serial No. 4205000 and Above)

On some snowmobiles, wear strips (D-70727)

of

installation
4"

(10.16cm) forward

dimension exactly may result in damage

track studs

is

de:;lrcd. Make certain

of

FRONT wear strip attaching hole

to

the

"Tipsters"

copy

Dept., P .0.

that

440

in

the

that

chassis tunnel with track studs installed.

a.re in numerical

you

receive is (example)

issues (75-1

you

the

and

75-2)

-

Box

1108,

Fond

du

N

0.

7

received. /

S/T

chassis tunnel will require repositioning if

FRONT END

and 440 T

of

both

in

chassis. Failure

5-8

/T

wear strips extend

to

(J2 I 6 I 7

observe this

4}

•

not

If wear strips are

1. Remove seat cushion, fuel

2.

Drill

out

14

3. Reposition each wear strip so

attaching hole
for

each wear strip).

4. Install fuel

5. Attach wear strips with

6. Install slide suspension and readjust track tension and alignment.

correctly positioned, reposition

tank

and slide suspension.

rivets, which attach wear strips

that

the

in

chassis. Using wear strip

tank

and seat cushion.

14

rivets (C-17-71790).

front

as

as

follows:

to

chassis, and remove wear strips.

end extends

a guide, drill

13/64"

4"

forward

(5.16mm) holes

of

front

thru

wear strip

chassis

(7

'

l

I

~

\

l

}

I'd!!

S

no-

Twister I

Hi-Performance

Tipster

NOTICE:
order,

75-3 --and
advise Mercury Marine

lac.

Sno-Twister/Hi-Performance

starting

with

75-1.

you

desire previous

WI

54935,

and

Publications

give

the

If

the

first

first

"Tipster"

number

TRACK ''STUD'' INSTALLATION

1975 Models 340

S/T,

(Chassis Serial No. 4205000 and Above)

On some snowmobiles, wear strips (D-70727)

of

installation

4"

(10.16cm) forward

dimension exactly may result

track studs

is

deslred. Make certain

of

FRONT

in

wear

damage

strip attaching hole

to

the

"Tipsters"

copy

Dept., P .0.

that

440

in

the

that

chassis tunnel with track studs installed.

are in numerical

you

receive is (example)

issues (75-1

you

and

75-2)-

Box

1108,

Fond

du

N

0.

7

received. I

S/T

chassis tunnel will require repos1t1oning if

the

FRONT END

and 440

of

both

in

chassis. Failure

5-8

T/T

wear strips extend

to

{J2

I 6 I 7

observe this

4}

"

not

If wear strips are

1. Remove seat cushion, fuel
out

2. Drill

3. Reposition each wear strip so

attaching hole
for

4. Install fuel

5. Attach wear strips with 14 rivets (C-17-71790).

6. Install slide suspension and readjust

14 rivets, which attach wear strips

each wear strip).

correctly positioned, reposition as follows:

tank

and slide suspension.

to

that

the

front

in

chassis. Using wear strip

tank

and seat cushion.

as

a guide, drill

track

tension and alignment.

chassis, and remove wear strips.

end

extends

4"

13/64"

forward

(5.16mm) holes

of

front

thru

wear strip

chassis (7

-~I

I

)

Sno-

Twister I

Hi-Performance

Tipster

340

NOTICE : Sno-Twister/Hi-Performance
order,

sta

rting

75-

3 •• a

advise Mercury Marine

Lac,

S/T

nd

WI

54935

and 440

with 75-

you

,

1.

desire

and

If
previous
Publications Dept., P.O.

give

the

S/T

the

first

"Tipsters

first

copy

"Tipster"

number

" are in numerical

you

receive

issues (75-1

Box

that

you

received.

is
and

1108,

(example)

75-2)

Fond

du

-

No. 75-9 (12118/74)

DRIVE SHEAVE RAMPS

Suggested Dimensions for ''SUPER-MODIFIED'' Ramps

As a result

and

440

be used with green compression spring and optional weights (0146-135 for

440

for

Green compression spring,
instruction sheet are included in Drive Sheave Modification Kit (D-71711A 1

t---r--+--+--+--+--+-----+--+--t---r-

t---r--+--+---+--+----'1

of

factory testing , Mercury has designed a drive sheave ramp profile suitable

S!T "Super-Modified" Snowmobiles

S!T).

an

assortment

Profile

of

"Blank."Jla

Profile

of

"~er

Modlfied" flamp



- I 4

.620"~

(see

drawing below). This ramp profile

of

weights, a

Cent~~rlin

_

of

Hole

-~-+1-

------'1f---J~

set

Bolt_

I I I

-

L

--

I I I

of

"blank"

1.

8"

7"

1

·

1

-t

1.

6"

1.4"

--T- -'

1.3"

for

is

intended

340

S!T and 0146-123

ramps (hardened) and an

).

I

I

340

S!T

to

1.4"

-/

/,

~r-

/ I I

r--

--:----

Suggested Dimensions for

:

=

=-:::

.

820"-,..--

.

5"

340

S!T and

:

:I

:::j

---'----1----'"

.7"

.3

"

1----+--+---1-

-+-+---1--+--

_.._.___._

.4"

.

3"

.2"

440

SIT "Super-Modified" Drive Sheave Ramps

.1"

-1--.2"

-

I

-r o

.1"

(;

/

ACTUAL SIZE

l

I

)

Sno-

Twister I

Hi-Perfo

rmance

Tipster

NOTICE : Sno-Twister/ Hi-Performance ''Tip
numerica
(example) 76-3 --and you
76-2) --advise M
Fond

MERCURY

MODEL

NAME

ENGINE SPECIFICATIONS

Engine Manufacturer Kohler
Engine Model

of

Cylinders

No.
Engine Displacement
HorsepOwer
Type

of

Cooling

Bore

Stroke

Ignition
Min.

Compressed

Gasket Thickness

Compressed

Min.

Gasket Thickness

(DVolume

•

of

Head

Spark Plug Hole - Vertical

Head

Volume w/Spark

Plug

-on

Crankcase

Overall Length

Cylinder Bore Material
Depth·

Depth·

Depth-

Width
Width
Height

Height

Width

Width

Height
Height

Heoght

Weight - Piston Assembly

Overall

Height
Height
No.
Ring Type
Ring Thickness
Ring Width(s) 2.7/2.4mm

Crankcase

DBA
Head Pipe Length
Head

a Flat Plate

Volume

of

Topol Cylin

of

Bottom

Top

Top

Port

Port/Excluding Chamfer

Port/Top (Wide Part)

Port/Bottom (Narrow Part

Port/Including Chamfer

Port/ Excluding Chamfer

Complete

(thru

Crankshaft

Intake Port

Top

of

of

Exhaust Port

Top

of

of

Transfer Port(s)

of

Transfer Ports

of

Intake Ports

of

Exhaust

/Incl

uding Chamfer

of

Exhaust

of

Exhaust

of

Exhaust

of

Transfer Ports

of

Intake

ot

Intake

He

ight

of

Center)

of

Piston/Exhaust

of

Piston

of A ings

per Piston

Face

Level

Pioe Inside Diameter

MARINE-

Head

Base

to

Top

of

Cyl

inder

der to

Cylinder

to

Cylinder to

Piston

SidE

/In

take Side

to

Center

of

K340-2AS K440·2AS
2

339.
40@ 7000
Axial

60.0mm

60.0mm 60.0mm
WicoCD

0.7mm 0.7mm

0.3mm

12.7cc

18.5

310.0cc

109.0 + 0.5mm 109.0 + 0.5mm 109.0 +

Chrome Plated Alum.

92.5.!. l.Omm

33

47.3.!_1.2mm 47.3.!. 1.2mm

34.2+

42.0+

27.0.!. 1.2mm

26.5

42.0!.

N.A.

12.7 + l.Omm

24.5.:t0.9mm

24.0.!_0.7mm

240.

70.5;t0.8mm

65

63.0+
2

"L"

1.995mm

70.0!_0.5mm

78

(

2)

.563"

,

l o

rder,

starting w

ith

76-1. If the fir

desire previous

ercur

y Mari

ne

du Lac,

WI

54935

Publications Dep

and

give the first numb

CERTIFIED SNOWMOBILE SPECIFICATIONS

19

1976

T(T

340

Kohler

2

3cc

RPM

Fan

.:t

1.0cc 26.5

.0;t

1.2mm 33.0.!. 1.2mm

1.0/14.1 + 1.0mm 33.8 + 1.0/12.8 + 1.0mm

0.8mm

.!_

0.7mm 26.5.!_0.7mm 30.7 .:t0.7mm

0.5mm

2g

.:t

10%

.0.!_

0.8mm

0.8mm

and Rectangular

.t_2

4

.0" + 0.192"

+ 0.02

5"

435.8cc 250cc
50@ 7000
Axial

68.0mm

Wico

0.3mm

21.7cc 10.5cc

310.0cc 305.0cc

Ch

92.5

48.0+0.8mm

27.0.!. 1.2mm 31.2_!1.2mm

42.0.!_0.5mm

N.A. 28.0.!_0.5mm

12.7 + 1.0mm 13.5 + l.Omm

24.5.:t0.9mm

24.0.:t0

335g.:t

71.7

65.0+

65.0!_0.8mm
2
"L"

"L"/2.515-R

3.0/2.7mm 2.12mm 2.6mm

70.0.:t0.

78 + 2

(

2)

1.563" + 0.02 5"

76 1976

440

TfT

RPM

Fan

CD

.:t

1.0cc

rome Plated

;t

l.Omm

.7mm

10%

.:t

0.8mm

O.Smm

and Rectangul

ectJ1.995m

5mm

4

.0"!.

0.192" (3)

Alum.

ar

sters" for

st

''Tipster"

copy

issues (76-1

1976

you

are

receive

in

is

and

No. 76-1 (11126175)

t., P .0. Box 1108,

er t

hat

you

received.

1976

250 SfT

Kohler
250 RLC
2

N.

A.

liquid

51.5mm

60.0mm
Thunderbolt

0.7mm

0.2mm

10

.7

Chrome Plated

93.9±.

28.7 ± 1.2mm

46.5_!1.2mm

27.7.!. 1.0/10.7 + 1.0mm

40.0_!0.8mm

32.0!.

30.9_!0.9mm

30.4 _!0.7mm 30.0_!0.7mm 33.5.:t0.7mm

198.0.!. 10.0g 240.0.!.

68

.7

65.0+0.8mm

63.0+0.8mm
1

"L

.. · Keystone

n 1.995mm

70.0;t0.5mm

78.±.2

1.5" + 0.02"

CD

.:t

0.8cc 17.5

O.Smm

Alum.

1.0mm

0.5mm

;t0.8mm

1.5"

!.

0.192"

340 SfT

Kohler

340

RLC

2

339.3cc
N.A.
liquid

60.0mm 68.0mm

60.0mm

Thunderbolt

0.7mm

0.3mm

14.2cc

305.0cc

109.0 + 0.5mm

Chrome Plated

92.5±

29.5±

46.5±

32.3 + 1.0/12.5 + 1

44.0_!0.8mm

30.5.!. 1.2mm

30.0.:t0.7mm

42.0.!_0.5mm 42.0.!_0.5mm

35.0_! 0.5mm 35.0.±_0.5mm

13.5 + 1.0mm

30.5.:t0.9mm

67.15;t0.8mm

62.0+0.8mm

60.0+0.8mm
1
"L"

1.995mm 2.515mm

70.0.±_0.5mm

78.!

(3) 1.5".:!:.

1.625'

CD

.:t

0.8cc

Alum.

1.0mm

1.2mm

1.2mm 46.5.!. 1.2mm

.Omm

lO.Og

- Keystone

2

0.192"

+.

U.02'

1976

440 SfT

Kohler
440 RLC
2

435.8cc

N.A.

liquid

60.0mm
Thunderbolt

0.7mm

0.3mm

16.5cc

23.5

305.0cc

109.0 + 0.5mm
Chrome Plated
9G.O.:t

28.6.!. 1.2mm

32.1.!. 1.0/15.2 + 1.0mm

42.0+0.8mm

31.0.!. 1.2mm

30.5_!0.7mm

13.5+

34.0.!_0.9mm

309.0

70.7

64.0+0.8mm

62.0+

1

"L

J.Omm

70.0;t0.5mm

78.±.2

(

3)

1.625' +. U.02''

.:t

l.Occ

1.0mm

l.Omm

.±.

10.0g

;t0.8mm

O.Smm

·Keystone

1.5"

+0.192"

CD

Alum.

(j)

Piston @ TDC

® Y -Pipe Manifold with Single Expansion Chamber and Muffler Assembly

®Twin

Expansion Chambers Discharg

ing int

o Single Muffler

OVER)

(

=

N.A.

NOTE:

Not

Applicable

See

Bottom

for

Metric/U.S. Conversion

of

Page

2

470"

XXXX

RPM

!_.12'

"!:

;!:..

:!:.

2"

.005"

.040"

.250'

.250"

:!:.

1976

340

TIT

· 077

:!:.

200

010"

015

.500"

.l;t~··

.250"

.125"

.125"

88.00" :!:.

28·36

365:!:. 151bs.

MODEL

NAME

CARBURETOR

Make/Model No.
No. per Engine

Venturi · Smallest 0 iameter

in

Throat

Throttle

Bore·

Downstream

Choke Yes Yes Yes

DRIVE CLUTCH

Make/Model No. Arctic
Engagement Speed
No.

of
Spring Wire Diameter
Drive Clutch Spring ·

Free Length

of

No.
Drive Clutch

Outside Diameter
Arm/Roller Weight
Drive Clutch · Roller

Diameter

DRIVEN CLUTCH

Make/Model No.
Quantity/Driven Clutch

Spring(s)
Spring Wire Diameter
No.

of

Driven Clutch

Free Length
Ramp Angle

CHASSIS/SUSPENSION

Chassis Model
Suspension
Overall Vehicle Length 99.44":!:.
Chassis Length
Ski Length
Overall Vehicle Width
Sk

i Width

Center Distance between Skis

TRACK

Material Rubber /Steel Bars Rubber/Steel Bars

Width

Pitch Length 110.88" 110.88" 102.00"
Track Drive Sprocket Teeth 9 9
Id

ler Diameter

CHAINCASE

Standard Drive Sprocket 17 18 14

No.
Standard Driven Sprocket

No.

Optional Drive Sprockets

No.

Optional Driven Sprockets

No.
Drive Chain/Rows

WEIGHT

Overall (Less Gas) 365:!:. 151bs.

Largest Dia.

of

Butterfly

Springs/Color

Turns 3.9 3.9

Spring·

Turns

Spring·

of

Teeth

of

Teeth

of

Teeth

of

Teeth

Mikuni/V M32·91
2 2 2

32.0mm 36.0mm

33.0mm 37.0mm

3200
1tBiue

.192"!

2.49'

2.31

27.8;t2.0g
.

Arctic XXXX ·

1 1

.156" + .005" .156"
5 5

5.00'

30":!:.

74001 74001 74558
Slide Rail

88.00 +

;${.:>~)'

39.509"!

4.62";!:. .060" 4.62";!:..060" 4.06":!:. .08"
;ss.OO" +

15.00"+

7.625"

34 34

12·13·14·15·16-18

.

28·36

2 2

1976

440TIT

Mikuni/VM36·34 Mikuni/VM34

XXXX · 080

Arctic
3200

RPM + 200

1ttltue
.192"

+ .

005"

.12"

2.49":!:.

2.31":!:. .

040"

33.9

z2.0o

.470".!. .010"

Arctic

XXXX

· 015

+ .

005"

5.()(l":!:.

250"

30":!:.

2"

Slide Rail Slide Rail

99.44"!

.500"

.250"

37.500" + .125"

39.500" + .250"

;s:..w·

;!:..ll~··

15.00";!:..125" 15.00" +

7.625" 7.625"

12·13·14·15·16-17 12·13·15·16·17·UI 12·13·14·16-17·18

1976

250 SIT

34.0mm 36.0mm

34.5mm 37.0mm

Arctic

XXXX · 01:11

4000

RPM
1/Green 1/Green
.192.:!:. .005"

4.375'

:!:.

.250'

5 5

2.375":!:.

.040"

28.34

+.

:l.Ug

.010"

.470":!:.

Arctic

XXXX · 01

1 1

.156" + .005"
5

5.00":!:. .250" 5.00":!:.

30"!

20

89.875":!:.

82.875"

33.500" + .250"

39.250" + .250"

35.00" + .125"

Rubber/Grouser Rubber/Grouser

12

34 34

28·36

2 2

330+

101bs.

15 Arctic XXXX •

.250"

+ .2

50"

.125"

5

Slide Rail

89.875"!

82.875" + .250"

33.500" + .250"

39.250" + .250"

4.06" + .06"

35.00".!.

15.00";!:..125"

102.00"
12

7.625"

15

28-36

330 + 10

1976

340

Mikuni/VM
2

Yes

Arctic

XXXX

4000

RPM

.HI:.!'

;!:..I.Xr.)·

4.;$1~'

:!:.

.:t:.u•

2.375"!

.040"

l~.;stl

+.

:t.ug

.470".!.

.010"

.156" + .005"

.250"

J00+20

74558

.250"

.125"

lbs.

SIT

36

• 088

015

1976

440

SIT

Mikuni/VM38
2

37.5mm

38.0mm

Yes

Arctic XXXX · 089

4000

RPM

1/Green

.192'

.!_.005'

4.;st~·

:!:.

.l~u·

5

.040"

2.375":!:.

28.34!:

2.0g

.470":!:. .010"

Arctic XXXX · 015

1

.156" ± .005"
5

5.00"!

.250"

JOO+~

74558
Slide Rail

89.875" + .250"

82.875" + .250"

33.500" + .250"

39.250" + .250"

4.06";t.06"

35.00" + .1

Rubber/Grouser

15.00" + .1

102.00"
12

7.625"

16

34

12·13·14·15-17·18

28·36

2

330 + 10

25"

25"

lbs.

'

METRIC/U.S. CONVERSION: 1mm (millimeter)=

1cc

(cubic centimeter)=

0.0394"

0.06

(inch);

cu.

in.;

1"

= 25.4mm;

1 lb. (pound)

11

g (gram)= 0.04oz.;

•=

0.4536kg (kilogram)

Sno-

Twister I Hi-Performance Tipster

NOTICE: Sno-Twister/Hi-Performance

numerical

(example)

76-2)

Fond

order,

76-3

--advise

du

lac,

starting

54935

you

with

desire

and

--and

Mercury Marine

WI

76-1.

give

"Tipsters"

If

the

previous

Publications

the

first

"Tipster"

number

first

Dept.,

for

copy

you
issues (76-1
P.O.

that

1976

Box

you

are

in

receive is

and

1108,

received.

No. 76-2 (11126175)

SET-UP INFORMATION

''Stock''

IGNITION TIMING

Standard ignition

Manual") MUST

are

will

easier

specification

SPARK PLUGS

Standard spark plugs (Champion ON-19V) MUST BE USED FOR RACING. Champion N-55G plugs

(which

- 1976 Model 250-340-440

timing

BE

gain absolutely nothing and could

to

"read")

for

each

model

(as

specified in the

ADHERED TO. Advancing ignition

cause

may

be

used

to

determine correct carburetor

S/T

Sff

timing

Snowmobiles

"Operation and Maintenance

beyond the recommended

serious engine damage.

"jetting"

ONLY.

CYLINDER HEAD - "SQUISH" CHAMBER CLEARANCE

A

MINIMUM

dome [heads torqued

C)].

(430

1.

Place a piece

of

.030"

When re-using

of

L-shaped, soft, wire solder through the spark plug hole

(0.76mm) clearance must

to

225 in. lbs. (259kg-cm) after engine warmup

head

gaskets, check

be

"squish"

maintained between cylinder

chamber clearance

to a minimum

as

to

2. Rotate engine over TDC.
of

3. Remove and measure flattened section

wire solder.

COOLING SYSTEM

• When installing cylinder heads, a
the cylinder

If

coolant leakage should occur

•
and apply

head

gaskets.

GE

Silicone Sealer

• In extreme cold temperatures,
maintain the recommended engine operating temperature [above 1100 F (430

• Frequently check and tighten all hose clamps.

thin

film

of

GE

at

cylinder

to

the stud threads and

it

may

head

be

necessary

Silicone Sealer should

be

mounting studs, clean the mounting hardware

bosses

to

on the cylinder

"tape

off" a portion

head

and piston
of

follows:

the cylinder wall.

used

on both

heads.

of

the radiator

C)

MINIMUM).

110°

sides

F

of

to

CARBURETORS

440

SIT

Engine idle = 3000

Calibration =

S/T

340

Engine idle = 3000

Calibration = No

250

S/T

Engine idle = 3000

Calibration = CHANGE

No

change

change

from

RPM

from standard settings

RPM

from standard settings

RPM

jet

needle E-rings from 2nd groove

top.

TORQUE SPECIFICATIONS

Torque

Cylinder
Crankcase halves (only)

Cylinder head . . . . . . . . . . . . . .

Rotor
Screws
Retractable starter
Drain plug
Exhaust flange
Spark plug

block

nut

to

water pump cover . . . . . . . . . . . . . . .

.

...

..........

............

........................

....................

.....................

..

Specs

.....

..

from

top

to

4th

groove

250

S/T

185 in. lbs.

.

.

.

......

. .

..

. .

.
.

155 in. lbs.

225 in. lbs.

90ft.

lbs.

95 in. lbs. 95

85

in. lbs.

95

in. lbs.

85

in. lbs. 85 in. lbs.

18ft.

lbs.

340

S/T & 440

225

225 in. lbs.

in. lbs.

155 in. lbs.

90ft.

lbs.

i11.

lbs.

85

in. lbs.

95

in. lbs.

18ft.

lbs.

S/T

(1

in.

lb.=

1.15kg-cm;

1ft.

lb.=

.14mkg)

THROTTLE CABLES

Occasionally lubricate

1.

Lubricate
Drill

2.

a 1

from

/16"

throttle

ends

of

cables around core wires, and/or

(1.6mm) hole

cable core wires

in

top

end

of

cable junction block and lubricate through the hole.

with

WD40

or

LPS

lubricant.

CLUTCHING

To

obtain and maintain ultimate snowmobile performance, proper clutch operation is a

maintaining peak engine operating RPM.

1.

Use

drive belt D-57-74294 (identified

2. 250

3.

4. Frequently disassemble, clean and inspect drive clutch assembly - once every

SIT

- adjust driven
acceleration.
340

SIT -

440

SIT

W.O.T. acceleration.

recommended.

IMPORTANT:
PARTICULAR
cover
clutch

is

is

removed

To

CARE

removed and/or installed. This task is made somewhat easier

from

sheave

- adjust driven

prevent scarring

to

keep cover

the engine before disassembly.

by

white patch on belt cover).

spring preload

sheave

spring preload

or

chipping the inside diameter
"SQUARE"

to

achieve 9200

to

on shaft (prevent cocking and binding),

to

9500 engine

achieve 9250

of

the cover bushing,

RPM

to

9500 engine

if

the complete drive

"must"

at W.O.T.

RPM

race

day is

TAKE

in

at

as

During each inspection,

recognize and replace roller assemblies with worn bushings will lead

be

certain

to

inspect

the

bushings

in

all

of

the roller assemblies. Failure

to

premature ramp destruction.

to

NOTE:
(not

~1'--

Construction and

to mention an

Round

''A''

3/8"

aid

the

Edges

(9.5mm)

to

use

of

your

sanity) when removing and installing the

.-570-"~J

.580"

I~

SCALE

the simple

G::~::)

SKI ASSEMBLIES

1. Check
grind

2. Check
the
as required.

both

leaf springs

or

file the sides

the

"curl"

shock absorber when

of

of

the leaf spring (top forward end)

to

make certain

the

spring, as required.

the

spring

tool

1"

(25.4mm) Approx.

-1:1

that

they move freely

is

collapsed.

(sketched below)

Material:
3/16"
Thick Steel

to

If

necessary, grind

(4.8mm)

in

make sure

is

an unbelievable time-saver

roller

assemblies.

Insert Tang
between Roller
and Twist Tool
to

Spread Arms.

the plastic slides.

that

the

"curl"

or

file end

of

If

necessary,

does

spring

''A"

Arm

not

"curl",

hit

c CARBIDE SKEGS

Starting with Standard Carbide Skegs D-74783-1 (ten,
front

to

rear) -

Move

1.

2. Depending upon conditions and individual preference,

SUSPENSION ADJUSlMENTS

Initial suspension settings should be:

1.

2. Set the springs
Weight transfer effect can be increased by increasing

suspension).
Weight transfer effect can

chassis

carbide segment Nos. 1 and No. 2 behind No.

10.

carbide segments; one behind No. 3 and one behind No.
carbide skeg] .

Front

arm

in

upper chassis hole and middle hole

quite

or

upper hole

NOTE:

Less

in

weight transfer

stiff.

be

decreased by decreasing

suspension).

effect

results

in

on

the

more

1"

carbide segments; numbered 1-thru-10,

3.

Move

No. 4 carbide segment behind No.

you

also may want

10

[4"

and

the

suspension.

angle

of

the

front arm (lower hole

the

angle

of

the

ski

pressure while accelerating.

to

add

8"

(10cm and 20cm)

front

arm (lower hole in

two

more

in

1"

the

TRACK

Handling on hard ice appears best when track
track bands and scat studs (or "claws") scattered across

"STUDDING"

is

studded generously with carbide studs on

the

center track band.

the

outer

hl

,__),

1

1

,

~

I

Sno-

Twister I Hi-Performance Tipster

NOTICE: Sno-Twister/Hi-Performance
numerical
(example)
76-2) •· advise Mercury Marine
Fond

IMPORTANT:

order,
76

-3

··and

du

lac,

WI

250

S/T

Modification

starting

with 76·

you

desire

54935

and

give

MODIFICATION INSTRUCTIONS

of

exhaust system and/or engine VOIDS

"Tipsters"

1.

If

the

previous

Publications

the

first

"Tipster"

number

first

Modification instructions are intended solely

CAUTION:
following.
PARTS

Modify

ANY

NOT

MENTIONED

engine, exhaust system and carburetion

DEVIATION

from

WILL

SPECIFIED DIMENSIONS

DECREASE PERFORMANCE and could result

engine damage.

Modifying 250

S/T

from

"Stock"

for

1976

copy

you

receive is

issues (76-1

Dept.,

P.O.

Box

that

you

received.

for

race applications.

are

in

and

1108,

to

No. 76-3 (R1-1211175)

your

WARRANTY.

EXACTLY

or

MODIFICATION

as

"Modified-Stock"

instructed,

of

in

severe

ENGINE

A. Cylinders

1.

Exhaust

a.

Raise
(Figure

b. Square

ports) while increasing chordal

(12.70mm) radius in side

ports) and continue side

NOTE: Chordal
following

c.

Change radius
After

d.

(Figure

e.

Remove sharp

fine

Port-

Enlarge exhaust

top

edge

of

1)

DO

NOT

off

side

edges

width

curvature

of 2 top

grinding exhaust

1)

DO

NOT

edges

emery cloth.

and "Super-Modified"

port

of

each

exhaust

change

of

exhaust

port

bottom

edges

edges

(Figure

of

cylinder wall).

exhaust

port,

chamfer side

from

exhaust

cylinder

to a point

edge

of

port

(down

width

of

port

make a 0.

of

port

of

exhaust

port

over

1)

is straight line distance between side

corners

060"

edges

or

bottom

port

by

as

follows:

1.100"

(27.94mm) below

exhaust port.

to a point

to

1.438"

port

(at a

to

bottom

to

0.20"

( 1.52mm) chamfer

edge

lightly

rounding cylinder bore

top

surface

directly

opposite

(36.00mm). (Figure
point
edge

directly

of

port,

opposite

as

shown in Figure 1.

edges

(5.08mm). (Figure 1)

to

top

edge

of

port.

of

top

of

1)

Cut a 0.50"

top

of

of

exhaust port.

edges

of

cylinder.

transfer

of

transfer

port

port

(not

with

Reduce
Required
Cover

Piston

Piston

Is

(Bottom

IN

Square
Port

(Down

Top

of

Increasing

~

Boss

to

to

Completely

Ring

at

BDC

Dead

Center)

Make a 0.060"

Off

Side

to a Point

Transfer

Chordal

Raise
below

Minimum

When

Cut

Port
at a Radius
of

0.20"

Edges

Ports)

Width

Exhaust

Top

Surface

41nlet

Corners

Chamfer

of

Exhaust------.

Directly

While

Opposite

to

EX

Port

to

1.100"

of

Cylinder

,---+----..

Lower

Inlet

Port

to

3.779"

below

Top

Surface

of

Cylinder

Make a 0.060"

I (

Chamfer

1-,

Edge
Port

~~~~--------~

1

This

'--.-.:-....-:-~

Edges
Port
Directly

Top

Ports

IN

Point

of

Must

of

Transfer

to

Top

of

Exhaust

t

f

....-::

on

Side

Exhaust

Be

Opposite

-

~-~

I

E X

Change

2

Top

-,<

Cut

a

~

Side

Edges

Port

(at a Point

Opposite

Ports)

and

Side

Edges

over

to

Radius

Exhaust

Radius

of

Top

Continue

of

Bottom

of
Port

in

Exhaust

Directly

of

Transfer

Port

Edge

j

~_)

Port-

2. Inlet
a.

Lower

Enlarge
bottom

cylinder. (Figure 1) DO

Cut

b.
c.

d.

e.

4 inlet
Reduce
to
After

(Figure

boss

completely cover piston ring when piston is

grinding

1)

Remove sharp

fine emery cloth.

IMPORTANT: DO

B. Ignition Timing
Retard ignition

timing

Figure 1. 250

inlet

edge

port

corners

at

top

inlet

DO

NOT

edges

to

16.00 BTDC@ 3000

port

of

each

of

inlet

NOT

at

a radius

edge

of

inlet

port,

make a

chamfer

from

NOT

side

inlet

POLISH transfer

SIT

..

Modified-Stock" Cylinder Dimensions

cylinder

port

change

of

port

as

follows:

to a point

top

edge

0.20"
to

a minimum. (Figure

3.779"

or

chordal

(5.08mm). (Figure 1)

at

BDC (bottom dead center).

(95.99mm) below

width

0.060" (1.52mm) chamfer

edges

or

top

edge

of

port.

port

by

lightly rounding cylinder bore

passages.

RPM

····------····Shape

--------Shape

of

inlet

port

.

1)

Boss

must

to

bottom

edge

edges

of

"Stock"

of

Modified

top

surface

be

large enough

of

inlet

of

port

Ports

Ports

of

port.

with

IMPORTANT: Ignition timing

characteristic

applicable

of

ONLY

this ignition system). For this reason, the

at

3000 RPM and is equivalent

EXHAUST SYSTEM

NOTE:
you

meet

When

removing parts (muffler,

are making the machine lighter. A certain

weight

limit.

will

retard slightly

air

intake

as

engine

RPM

timing

to

130 BTDC@ 9250 RPM.

box,

etc)

from

snowmobile, keep in

amount

of

weight

may

increases

specification

have

to

be retained to

(a

normal

of

160 is

mind

that

Replace

obtain ordering

"stock"

exhaust system

information

CARBURETION

1. Remove carburetor

2. Remove large

air

funnel

with

modified exhaust pipes (available

on modified pipes, contact:

Mercury Marine
Hi-Performance Products Department
20

Wisconsin Street

Oshkosh, Wisconsin 54901

Attention:

Telephone: [phone]

air

intake

from

box

from

each

carburetor.

snowmobile.

thru

Snowmobile Division

Mercury Marine).

To

NOTE:
you

meet

3. Check synchronization

4. Check carburetor adjustments (idle
jets).
of

NOTE:

a

When removing parts (muffler,

are making the machine lighter. A certain

minimum

CAUTION:
setting. Carburetors, which are adjusted
damage.

Adjust

spark plugs.

Use

"stock"

high

fixed

250

weight

When in

SIT.

limit.

of

carburetor

doubt

speed

mixture

high speed jets which are 1

about

(replace

DRIVE SYSTEM

A.

Maximum

"modified-stock"

A
9,900

throttle

RPM

("running

engine

Engine RPM

and

on"

RPM

to

this

"super-modified"

to

10,200 RPM).

speed.

air

intake

throttle

a carburetor adjustment,

speed,

fixed

250 SIT

box,

etc)

amount

valves and readjust

too

low

speed

high

to 2 jet

will

Modify

of

"lean",

mixture,

speed

sizes larger (richer) than those required

deliver maximum

and adjust

from

snowmobile, keep

weight

will

jets)

may

as

necessary.

ALWAYS

cause

jet

needles and fixed high

to

achieve

torque

have

to

select a

severe

power

converter

internal engine

"normal"

when operated at

in

mind

that

be retained to

"richer"

speed

coloration

for

to

increase

full

r

B. Drive

Install Drive

correct

C. Sprockets

Snowmobile may require "re-gearing"
exhaust

operating conditions)

Sprocket

Sheave

full

throttle

NOTE:

Clutch

modification).

Chart",

(Clutch)

Sheave

modification

following.)

Modification

engine

RPM

Installation

to

change

Kit

(as

recommended in preceding paragraph) and desired

instructions are supplied

of

top

speed

(D-71711A2).

because

another driver sprocket may

of

snowmobile (MPH) and acceleration. (Refer

Modify

of

increased horsepower

profile

with

modification

of

drive

be

desired (depending upon

sheave

kit.

(a

result

ramps

shift

of

engine and

to

obtain

pattern.

to

"Driver

Top

Speed

DRIVER

of

Snowmobile {MPH)

High

MPH

Low

MPH

SPROCKET CHART

No.

of

Teeth Part Number

18

17
16 D-69757A16
15 D-69757A 15

14.
13
12

D-69757A18

D-69757A17

D-69757A 14 •
D-69757A 13
D-69757A12

• Standard (factory installed)

BREAK-IN PROCEDURE

After

modifying
throttle
temperature)

(50%

for

an

S!T Snowmobile

to

75% power)

"Break-

In"

and

250

and

prior

to

racing, the engine should

for

one

hour. Operate engine

all operation thereafter.

SIT

driver

sprocket

at

11QOF

be

"run

in"

to

1700F (coolant

at

part

Sno-

Twister I

Hi-Performance

Tipster

NOTICE: Sno-Twister/Hi-Performance

numerical
(example}
76-2} -- advise Mercury Marine Publications

Fond

340

IMPORTANT: Modification

Modification instructions

CAUTION:
following.

PARTS

engine

Modify

ANY

NOT

damage.

MENTIONED

order,

76-3-

du

lac,

WI

S/T

are

engine, exhaust system and carburetion

DEVIATION

Modifying 340 S/T

CYLINDERS

starting

and

you

54935

with

76·1.

desire previous

and

give

the

''Tipsters"

If

the

''Tipster"

first

number

first

Dept.,

for

copy

you
issues (76-1
P.O. Box

that

1976

you

are

in

receive is

and

1108,

received.

No. 76-4 (1211175)

MODIFICATION INSTRUCTIONS

of

exhaust system and/or engine VOIDS

intended solely

from

SPECIFIED DIMENSIONS

WILL

DECREASE PERFORMANCE and could result in

from

for

race

applications.

"Stock" to "Modified-Stock"

EXACTLY

or

your

as

MODIFICATION

WARRANTY.

instructed,

of

severe

c

A.

Exhaust Port

Enlarge exhaust

1.

Raise

. (Figure 1) DO

2. Square
(Figure 1)

NOTE:
following curvature

3.

Change

4. Enlarge radius

After

5.

exhaust port. (Figure 1) DO

6. Remove sharp

emery cloth.

port

of

top

edge

of

NOT

off

side

edges

Chordal width (Figure 1) is straight line distance between side

radius

grinding exhaust

of 2 top

of 2 bottom

edges

each

cylinder

exhaust

change

of

from

port

bottom

of

exhaust

cylinder wall).

exhaust

exhaust

port,

NOT

exhaust

as

follows:

to a point

edge

port

port

corners

port

make a

chamfer

port

1.100"

of

exhaust

while maintaining a chordal

to

corners

0.060"
side

by

lightly

(27.94mm) below

port.

0.20"

(1.52mm) chamfer

edges

(5.08mm). (Figure 1)

to

0.50"

rounding cylinder bore

(12.70mm). (Figure 1)

of

exhaust

port.

width

to

top

top

of

and

edges

surface

~~~

edges

bottom

of

port

of

cylinder.

(42.00mm).

of

port

(not

edges

with

fine

of

c

Reduce
Required
Cover

Piston

Piston

Is

(Bottom

Boss

to

to

Completely

Ring When

at

BDC

Dead

Minimum

Center)

IN

Bottom

Raise

to

1.100"

Edge

Exhaust

below

of

Inlet

EX

Port

Top

Port

Lower Inlet

~"below

Surface

of

Port

to

Top

Cylinder

Make
Chamfer

Edge
Port

Make
Chamfer

a

Q..QRQ"

to

of

Exhaust

a~"

to

Bottom

Enlarge
Exhaust

Top

E x \

Radius

Port

Corners

Change

Radius

Top

Exhaust

Corners

to

of 2 Bottom

to

0.50"

Port

0.20"

of

2

Square

Off

Side Edges

White Keeping a

of

Chordal

Figure 1.

Exhaust

Width

Port

__

__J_...__,.

of

1.654"

'

340

SIT ,.Modified-Stock" Cylinder Dimensions

B. Inlet Port

Enlarge inlet

1.

Lower
(Figure 1)

Cut 2 bottom

2.

3. Reduce

port

bottom

DO

boss

at

of

each

edge

NOT

inlet

top

cylinder

of

inlet

change

port

corners at a radius

edge

of

as

port

top

inlet

follows:

to a point

edge

or

port
completely cover piston ring when piston
After

4.
(Figure

5. Remove sharp

grinding inlet

1)

DO

NOT

edges

port,

chamfer

from

make a

side

inlet

port

0.060"

edges

by

emery cloth.

IMPORTANT: DO

NOT

POLISH transfer

EXHAUST SYSTEM

NOTE:
you are making the machine lighter. A certain
meet

When

minimum

removing parts (muffler,

weight

limit.

__

3.779"

chordal

of

0.20"

to

a minimum. (Figure 1)

is

at

BDC (bottom

(95.99mm) below top surface

width

of

inlet port.

(5.08mm). (Figure 1)

(1.52mm) chamfer

or

top

edge

of

inlet

lightly

rounding cylinder bore

passages.

air

intake box, etc)

amount

-------Shape

----Shape

Boss

dead

center).

to

bottom

port.

from

snowmobile, keep

of

weight may have

of

"Stock"

of

Modified Ports

Ports

of

cylinder_

must be large enough

edge

of

inlet

port.

edges

of

port

with

fine

in

mind

to

be retained

to

that

to

Remove

A.

1.

muffler

assembly

from

Exhaust Pipe Diverging Cones

Cut

0.75"

(19.05mm)

from

snowmobile

diverging cone

(Figure 2)

2. Weld header
not

restrict exhaust.

diverging cone

of

each

joint

to

3. Reposition spring hooks on exhaust pipes

and

modify

of

exhaust pipe.

to

give sufficient spring tension.

"stock"

each

exhaust pipe directly behind header

exhaust system

Be

sure

that

welds

as

follows:

are

smooth and do

joint.

_)

c

Cut

0.75"

Each

from

Exhaust

of

Behind Heeder

~~

Diverging

Pipe

(Directly

Joint)

and

Cone

Re-weld

c

Converging
(Rotate

1.00"1D

Modified--------+­Stingers

B.

Exhaust Pipe Center Sections

1.

Cut

0.50"

2. Before re-welding exhaust pipes, position pipes
fit.

3.

Weld

sections of exhaust pipes together.

exhaust.

C. Exhaust Pipe Stingers

1.

Cut production stinger from each exhaust pipe.

NOTE:
diameter

Converging cone

(I

Fit
and
Sections)

(12.70mm) from center section (at widest part)

D)

of

cones is enlarged

Cones

for

Best

in Snowmobile

Re-weld Center

Figure 2.

of

Weld

340

S(f

"Modified-Stock" Exhaust Pipes

exhaust pipes

to

1.00"

Be

may

(25.40mm)

of

each exhaust pipe. (Figure 2)

in

snowmobile and rotate sections

sure

that

welds are smooth and

have

to

be

cut

back

slightly

(same

ID

as

replacement stinger).

to

obtain best

do

not

so

that

restrict

inside

c

2.

Weld

modified stingers [1.00" I D x

1.02mm x 43.18cm) - Figure 2] to converging cones.

restrict exhaust.

0.040"

CARBURETION

1.

Remove carburetor air intake box from snowmobile.

2. Remove large air funnel from each carburetor.

NOTE:
you

meet

3. Check synchronization

When

removing parts (muffler,

are

making the machine lighter. A certain

minimum

weight

limit.

of

carburetor throttle valves and readjust

air

intake

thick (approximately) x

Be

sure

that

welds are smooth and do

box,

etc)

from

snowmobile, keep

amount

of

weight

as

necessary.

17

may

.00"

long (25.40mm x

in

have

to

be

mind

that

retained

not

to

CAUTION:
setting. Carburetors, which
damage.

When

in

doubt

about a carburetor adjustment,
are

adjusted

too

"lean",

will

ALWAYS

cause

severe

select a

internal engine

"richer"

4. Check carburetor adjustments (idle
jets). Adjust high
of

spark plugs.

NOTE:
a

"stock"

Use

340

fixed

SIT.

speed

high

mixture (replace fixed high

speed

jets which are 3

DRIVE SYSTEM

A. Maximum Engine
A

"modified-stock"

on"

to

10,000 RPM).

this

speed.

B. Drive
Install Drive

correct

NOTE:

C.

Snowmobile may require "re-gearing"
exhaust modifications). Installation
operating conditions)

Sprocket

Sheave

full

throttle

Clutch

Sprockets

Chart",

Sheave

RPM

340

SIT

Modify

(Clutch)

Modification

engine

modification

following.)

RPM

to

change top

will

deliver maximum power when operated

and

adjust torque converter

Kit

(as

recommended in preceding paragraph)

instructions are supplied

of

speed

DRIVER

speed,

(D-71711A2).

another driver sprocket may be desired (depending upon

low

speed

to 4 jet

Modify

because

of

of

increased horsepower

snowmobile (MPH)

SPROCKET

mixture,

speed

sizes

to

with

CHART

jet

needles

jets)

to

achieve

larger (richer) than those required

increase

profile

modification

and

full

of

drive

acceleration. (Refer

and

"normal"

at

9.750

throttle

sheave

and

desired

kit.

(a

result

fixed high

RPM
engine

ramps

shift

of

engine

speed

coloration

("running

RPM

to

obtain

pattern.

to

"Driver

for

to

and

J

Too

Soeed

of

Snowmobile (MPH)

MPH

High

~

,

Low

MPH

• Standard (factory installed)

BREAK-IN PROCEDURE

After
throttle
temperature)

modifying

(50%

an

to

for

"Break-In"

SIT Snowmobile

75% power)

and

Modifying 340 S/T

A limited number

To

Marine.

obtain ordering information on these kits, contact:

No.

340

and

prior

to

racing, the engine should

for

one hour. Operate engine

all operation thereafter.

from

of

"Super-Mod

"Stock"

Kits"

of

Teeth

18
17
16 D-69757A16
15•
14

13 D-69757A13
12 D-69757A 12

SIT

driver sprocket

to

"Super-Modified"

are

available thru Mercury

Part Number
D-69757A18

D-69757A17

D-69757 A 15 •
D-69757A14

at

11QOF

be

to

"run

in"

17QOF

at

part

(coolant

Mercury Marine • Hi-Performance Products Department •

Wisconsin 54901 •

Attention:

Snowmobile Division • Telephone: [phone]

20

Wisconsin Street • Oshkosh,

Sno-

Twister I

Hi-Performance

Tipster

440

IMPORTANT:

Modification

CAUTION:
following.
PARTS
engine damage.

Modification

instructions are intended solely

Modify

ANY

NOT

MENTIONED

Modifying 440

NOTICE: Sno-Twister/Hi-Performance
numerical
(example)
76-2)
Fond

S/T

DEVIATION

S/T

order,

starting

with

76-3

··and

WI

you

54935

••

advise Mercury Marine Publications

du

Lac,

76-1.

desire previous

and

give

MODIFICATION INSTRUCTIONS

of

exhaust system

for

engine, exhaust system and carburetion

from

SPECIFIED DIMENSIONS

WILL

from

DECREASE PERFORMANCE and could result in

"Stock"

"Tipsters"

If

the

first

copy

"Tipster"

first

and/or

Dept.,

number

the

race applications.

to "Modified-Stock"

for

1976

you
issues (76-1
P.O.

Box

that

you

engine

are

in

receive is

and

1108,

received.

VOIDS

EXACTLY

or

No. 76-5

your

WARRANTY.

as

instructed,

MODIFICATION

severe

(12/l/75)

of

ENGINE

A.

Cylinders

1. Exhaust
a.

b. Increase chordal

c.

d.

e.

f.

Port-

Raise

top

(Figure

NOTE:
following

Change radius

Enlarge radius

After

grinding exhaust

exhaust

Remove sharp

fine emery cloth.

Enlarge exhaust

edge

of

exhaust

1)

DO

NOT

width

Chordal

curvature

port.

width

of

of 2 top

of 2 bottom

(Figure

edges

change

of

(Figure

cylinder

exhaust

port,

1)

DO

from

port

of

each cylinder

portto a point

bottom

exhaust

exhaust

make a

NOT

exhaust

edge

port

1)

is straight

wall).

port

corners

port

0.060"

chamfer side

port

as

1.100"

of

exhaust

to

1.772"

corners

by

lightly

(45.00mm). (Figure 1)

line

to

0.13"
to

(1.52mm) chamfer

edges

follows:

(27.94mm) below

port.

distance between side edges

(3.30mm). (Figure 1)

0.50"

rounding cylinder bore

(12.70mm). (Figure 1)

of

port.

to

top

!Qp

surface

and

bottom

edges

of

cylinder.

of

port

of

port

(not

edges

with

of

Reduce
Required
Cover

Piston

Piston

Is

(Bottom

Boss

to

to

Completely

Ring

at

BDC

Dead

Raise
below

Minimum

When

Center)

Exhaust

Top

Surface

Cut 4 Inlet

Port

to

1.100"

of

Cylinder

Inlet

Lower
below

Top

Surfa,ce

~-+~r

Port

to

3.829"

of

Cylinder

Make a

0.060"

Chamfer

r

Edge

____

Pgr,~t~!~~~-/

of

to

Exhaust

Top

Change
2

Top

Corners

Radius

Exhaust

to

0.13"

of
Port

I

2. Inlet
a.

Port-

Lower

cylinder. (Figure 1) DO
b. Increase chordal
c.

Cut 4

inlet

d.

Reduce

to

completely cover piston ring when piston is at BDC (bottom

e.

After

grinding

(Figure 1) DO

f. Remove sharp

fine emery cloth.

IN

Enlarge

bottom

port

boss

at

Bottom

Edge

Increase

Figure 1.

inlet

port

edge

width
corners
top

edge

inlet

port,

NOT

chamfer side

edges

from

of

NOT

of

at

of

Inlet

Chordal

440

SIT

of

each

inlet

change

inlet

a radius

of

inlet

make a

inlet

Port

Width

of

"Modified-Stock"

cylinder

port

port

of

port

0.060"
edges
port

as

to a point

top

edge

to

1.772"

0.13"

(3.30mm

to

a minimum. (Figum

(1.52mm) chamfer

or

top

by

lightly

Make a
Chamfer
Bottom
Exhaust

Increase Chordall Width
Inlet

Port

to

1.772"

IN

····-

---------

-----

Cylinder Dimensions

follows:

of

port.

3.829"

(97.26mm) below

(45.00mm). (Fiigure 1)

).

(Figur~e

1)

1)
dead

to

edge

of

port

.

rounding cyllinder bore

0.060"
to

Edge
Port

of

Boss

must

center).

bottom

EX

of

Shape

,

Shape

edge

edges

Enlarge

Radius

2

Bottom

Port

Corners

0.50"

of

"Stock"

of

Modified Ports

top

surface

be

large enough

of

inlet

of

port

of

Exhaust

to

Ports

of

port.

with

IMPORTANT: DO NOT POLISH transfer passages.

B.

Pistons

NOTE:

Remove

Inlet

0.060"

remove sharp

side

of

piston is side opposite exhaust mark on

(1.52mm) from

edge

from

skirt

inlet

by

cutting a

side

of

each

.005"

piston

piston skirt. (Figure 2)

( .13mm) radius on

edge.

dome.

After

cutting piston skirt,

IN

Figure 2.

440

EXHAUST SYSTEM

NOTE:
you
meet weight

Remove

A.

Exhaust Pipe Diverging

1.

Cut

(Figure 3)

2. Weld header
not

3. Reposition spring hooks on exhaust pipes

When

removing parts (muffler,

are making the machine lighter. A certain amount

limit.

muffler

1.00"

restrict exhaust.

assembly from snowmobile and

Cones

(25.40mm)

joint

from

diverging cone

to

diverging cone

of

air

each

Remove
from
of

___

-----Shape

SIT

"Modified-Stock"

intake box, etc) from snowmobile, keep in

of

modify

of

exhaust pipe.

to

give sufficient spring tension.

"stock"

each

exhaust pipe,

Piston

weight

exhaust system

Be

sure

that

0.060"

Inlet Side

Piston

Skirt

l

______

Shape

may

have to be retained to

as

follows:

directly

behind header

welds

are

of

"Stock"

of

Modified Piston

mind

smooth and do

Piston

that

joint.

Cut

1.00"

Cone

(Directly Behind Header

Joint)

for

Best

Center

Sections)

t

440

Weld

S

IT

"Modified-Stock"

j

\...-

Cut
Center

Exhaust Pipes

1.00"

Converging Cones

(Rotate

Fit

in

Snowmobile

and

Re-weld

Mod.;od~

Stingers

Figure 3.

from

of

Each

and

Re-weld

from

Section

Diverging

Exhaust

Pipe

B.

Exhaust Pipe Center Sections

1.

Cut

1.00"

(25.40mm) from center section (at widest part)

2. Before re-welding

exhaust

fit.

3. Weld sections

of

exhaust

exhaust.

C.

Exhaust Pipe Stingers

Cut

1.

production stinger from each exhaust pipe.

pipes, position pipes

pipes together.

Be

of

each exhaust pipe. (Figure 3)

in

snowmobile and rotate sections

sure

that

welds are

smooth

and

to

do

obtain

not

restrict

best

NOTE:
diameter

2. Weld modified stingers

1.02mm x 43.18cm) - Figure 2]

Converging cone

(/D)

of

cones are enlarged

[1.00"

of

exhaust pipes

to

ID x 0.040"

to

converging cones.

may

have

1.00"

(25.40mm)

thick (approximately) x

restrict exhaust.

CARBURETION

1. Remove carburetor air intake box from snowmobile.

2.

Remove large air funnel from each carburetor.

NOTE:
you
meet

3. Check synchronization

When

are making the machine

minimum

CAUTION: When in

removing parts

weight

limit.

of

carburetor

doubt

(muff

lighter

about

ler,

air

intake

. A certain

throttle

a carburetor adjustment, ALWAYS select a

setting. Carburetors, which are adjusted

damage.

box,

amount

valves and readjust as necessary.

too

to
(same

Be

sure

etc)

of

"lean",

be

cut

back

ID

as

replacement stinger).

17.00"

that

welds are

from

snowmobile, keep

weight

may

slightly

have

so

that

inside

long (25.40mm x

smooth

and

in

mind

to

be retained

do

"richer"

will cause severe internal engine

not

that

to

4.

Check carburetor adjustments (idle speed, low speed mixture,
jets). Adjust high speed mixture (replace fixed high speed jets)
of

spark plugs.

NOTE:
a

Use

"stock"

fixed

440

high speed jets which are 3

SIT.

to 4 jet

sizes larger (richer) than those required

DRIVE SYSTEM

A.

Maximum Engine

A "modified-stock"
on"

to

10,000 RPM). Modify and adjust

this speed.

B.

Drive Sheave (Clutch)

Install Drive Sheave Modification Kit (D-71711A2). Modify profile

correct full

NOTE:

throttle

Clutch

RPM

440

S/T

will deliver maximum power when operated

engine

modification

RPM

torque

(as recommended

instructions are supplied

converter

in

preceding paragraph) and desired shift pattern.

to

increase full

with

modification

jet

needles

to

achieve

and

"normal"

at

9,750

throttle

of

drive sheave ramps

kit.

fixed high speed

coloration

for

RPM

("running

engine

RPM

to

obtain

to

C.

Sprockets

Snowmobile may require "re-gearing"

top

DRIVER

MPH

of

speed

exhaust modification). Installation

to

operating conditions)
Sprocket

Chart",

Top

following.)

Speed

change

of

Snowmobile (MPH)

High MPH

1

Low

• Standard (factory installed)

BREAK-IN PROCEDURE

After
throttle
temperature)

modifying

(50%

for

an

SIT

to

75% power)

"Break-In"

Snowmobile and

for

and

all operation thereafter.

because

another driver sprocket may

of

one hour. Operate engine

of

increased horsepower

be

desired (depending upon

snowmobile (MPH) and acceleration. (Refer

SPROCKET

prior

to

CHART

No.

of

Teeth

18
17

16.
15
14 D-69757A14

13
12

440

SIT

driver sprocket

racing, the engine should

at

110°F

(a

result

Part Number
D-69757A18

D-69757A17
D-69757 A 16 •
D-69757A

D-69757A 13
D-69757A

of

15

12

be

"run

to

1700F (coolant

engine and

to

"Driver

in"

at

part

Modifying 440

A

limited

Marine.

To

S/T

number

from

of

"Super-Mod

obtain ordering

"Stock"

Kits"

information

Mercury Marine
Hi-Performance Products Department
20
Oshkosh, Wisconsin 54901

Telephone: [phone]

to

"Super-Modified"

are

available

for

these kits, contact:

Wisconsin Street

Attention:

thru

Snowmobile Division

Mercury

Sn

o-

Twister I Hi-Perf

orm

an

ce

Tipster

NOTICE:
numerical
(example)

76-2)

Fond

1976

MODB..S

REAR

Mercury Marine
on 1976 Model Sno-Twisters. The failure

Reinforce rear suspension control arm

If

A.

B.

track guide
(.100"/.125"
If

track guide HAS BROKEN loose

(1.90"/2.00"

control arm,

has

received a few reports

has

NOT BROKEN loose

thick

x

.50"

diameter x

as

shown in Figure 2.

Sno-Twister/Hi-Performance
order,

starting

76-3

Lac,

--and

Mercury

WI

54935

--advise

du

250

SUSPENSION

as

wide)

to

track guide

.50"

wide). Flatten tube

with

you

desire

Marine

and

S/T,

76-1.

give

"Tipsters"

If

the

previous

Publications

the

first

'"Tipster"

number

340

CONTROL

of

the rear suspension control arm (D-74492A 1) failing

is

occuring where track guide

follows:

from

control arm, securely weld a

and

control arm,

from

control arm, replace guide

to

first

copy

Dept.,

S/T

a height

for

1976

you
issues (76-1
P.O.

that

you

and

are

in

receive

is

and

Box

1108,

received.

No. 76-7 (12130175)

440

ARM

is

welded

as

shown in Figure

with

a piece

of

1.62"

and weld securely

S/T

to

the control arm.

steel

1.

of

steel tube

strap

to

Rear

Control

Figure 1. Reinforcing

Arm

Weld

Suspension

Arm

SCALE-

Rear

Suspension Control

%:1

Rear

Suspension

Control

Figure 2. Repairing Rear Suspension Control

Arm

Arm

SCALE:

%:1

..

'

·"

' .

Sno-

Twister I

Hi-Performance

Tipster

NOTICE:
numerical

(example)

76-2)

Fond

1976 MODELS 250

Sno-Twister/Hi-Performance
order,

starting

··

du

76-3

advise

Lac,

-·and

Mercury

WI

you

54935

with

desire previous

Marine

and

76·1.

Publications

give

the

S/T,

(Chassis Serial No. 4349324 and Above)

CHASSIS - FRONT CROSSMEMBER

Mercury Marine

1976 Model Sno-Twister snowmobiles

just

outside

ALL

CROSSMEMBERS MUST

further operation

1.

Remove

crossmember are evident, weld

2. Position a reinforcing steel strap [11
between lower bulkhead and crossmember. (Figure 1)

has

received a few reports

that

of

engine mounting tabs (either side).

lNG:

WARN

of

snowmobile. Reinforce crossmember

11

rivets which

Failure

secure

of

crossmember could result

BE

INSPECTED and REINFORCED

lower bulkhead

as

necessary

of

the chassis-front crossmember (D-74553A2) failing on

have

before installing reinforcing steel strap.

gauge

"Tipsters"

If

the

"Tipster"

first

number

been raced. The crossmember failure

to

(0.1196") cold rolled steel

for

1976

are

first

copy

you

issues (76-1

Dept.,

P.O.

Box

that

you

340

crossmember. (Figure 1)

as

follows:

S/T

in

receive is

and

1108,

received.

and 440

in

loss

of

steering.

IMMEDIATELY

No.

If

(1.00" x 30.50")]

76-8

( 1129176)

S/T

is

occuring

before

any cracks in

I

r--

Do

Not

Reinstall

l

Figure 1. Reinforcing Crossmember (Viewed

3. Securely weld steel strap
IMPORT

drill

ANT:

a rivet hole thru steel strap at these locations.

Outer rivets (one

~

to

crossmember

;·I

I

1"

=

2.54cm

ONLY

each

side - Figure 1)

11

Gauge (0.1196") Cold Rolled

26.00"

Steel Strap (

1.00" x 30.50")

--

13

.00"

-

21.00''

(1/8"

Wide x

from

at

locations shown in Figure 1.

will

not

be reinstalled, therefore, DO

1"

Weld

Both

(1/8"

Wide x

Underside)

Long)

Ends

%''long)

NOT

4. Using rivet holes
strap.

5.

Secure lower bulkhead

The Mercury Marine

of

Cost

this reinforcement is

in

lower bulkhead

to

crossmember

"Limited

Warranty" is

to

be

borne

as

a guide,
with

not

by

the owner.

drill

9 rivet holes

9 steel rivets (D-17-74671

extended

to

snowmobiles

(3/16")

).

(Figure

that

thru

reinforcing steel

1)

are

used

for

racing.

,-.-

t

"'\

..