Snowmobile Polaris EDGE / WIDETRAK (2007-2012 year). Instruction - part 22

 

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Snowmobile Polaris EDGE / WIDETRAK (2007-2012 year). Instruction - part 22

 

 

4.2

Fuel System

9923396 - 2007-2012 EDGE/Widetrak LX Service Manual

©2011 Polaris Sales Inc.

FUEL SYSTEM OVERVIEW

Warnings and Cautions

CARBURETOR COMPONENTS

Mikuni Pilot Jets

Mikuni Main Jets

WARNING

Always stop the engine and refuel outdoors or in a well 

ventilated area.

Do not smoke or allow open flames or sparks in or near 

the area where refueling is performed or where 

gasoline is stored or used.

Do not overfill the fuel tank. Do not fill up to the fuel tank 

filler neck.

If you get gasoline in your eyes or if you swallow 

gasoline, see your doctor immediately.

If you spill gasoline on your skin or clothing, 

immediately wash it off with soap and water and 

change clothing.

Never start the engine or let it run in an enclosed area.

 Gasoline powered engine exhaust fumes are 

poisonous and can cause loss of consciousness and 

death in a short time.

Always store fuel in an appropriate container, away 

from sources of heat. Never store fuel in a glass 

container.

Never ship a used fuel tank assembly. Always follow 

local and federal regulations with regard to proper fuel 

handling and disposal guidelines.

CAUTION

A main jet that is too small will cause a lean operating 

condition and may cause serious engine damage. Jet 

according to the jetting charts provided for each 

snowmobile.

Never use fuel containing more than 10% ethanol or E85 

fuels.

PILOT JET NUMBER

PART NUMBER

25

3130064

30

3130065

35

3130066

40

3130067

45

3130068

50

3130629

55

3130070

60

3130071

M

A

IN

 J

E

T

P

ART NUMBER

M

A

IN

 J

E

T

P

ART NUMBER

M

A

IN

 J

E

T

P

ART NUMBER

95

3130102

175

3130118

310

3130134

100

3130103

180

3130119

320

3130135

105

3130104

185

3130120

330

3130136

110

3130105

190

3130121

340

3130137

115

3130106

195

3130122

350

3130138

120

3130107

200

3130123

360

3130139

125

3130108

210

3130124

370

3130290

130

3130109

220

3130125

380

3130140

135

3130110

230

3130126

390

3130480

140

3130111

240

3130127

400

3130141

145

3130112

250

3130637

410

3130599

150

3130113

260

3130129

420

3130142

155

3130114

270

3130130

430

3130143

160

3130115

280

3130131

440

3130144

165

3130116

290

3130132

450

3130145

170

3130117

300

3130133

460

3130146

4.3

Fuel System

4

9923396 - 2007-2012 EDGE/Widetrak LX Service Manual

©2011 Polaris Sales Inc.

MIKUNI VM CARBURETOR

Assembly View

Mikuni VM Carburetor Function

The function of a carburetor is to produce a combustible
air/fuel mixture by breaking fuel into tiny particles in the
form of vapor, to mix the fuel with air in a proper ratio, and
to deliver the mixture to the engine. A proper ratio means
an ideal air/fuel mixture which can burn without leaving an
excess of fuel or air. Whether the proper mixture ratio is
maintained or not is the key to efficient engine operation.

The engine is operated under a wide range of conditions,
from idling with the throttle valve almost closed, to full load
or maximum output with the throttle valve fully opened. In
order to meet the requirements for the proper mixture ratio
under these varying conditions, a low speed fuel system,
or pilot system, and a main fuel system are provided in
Mikuni type carburetors.

A Mikuni VM carburetor uses several components and fuel
metering circuits to deliver fuel at all throttle opening
positions. These components and circuits include:

• Starting (Enrichment) Circuit

• Float System

• Idle Speed Adjustment

• Air  Screw

• Idle / Slow Speed (Pilot) Circuit

• Throttle Valve / Cutaway

• Needle Jet

• Jet Needle

• High Speed (Main Jet) Circuit

4.4

Fuel System

9923396 - 2007-2012 EDGE/Widetrak LX Service Manual

©2011 Polaris Sales Inc.

Throttle Opening and Fuel Flow

The illustration below depicts how each fuel metering
circuit effects the total fuel flow of the carburetor as well as
the fuel flow characteristics when the jet needle e-clip is
moved from position 2 to position 4.

This illustration can be helpful when trying to diagnose a
fuel-related problem when the throttle opening at which
the rich or lean condition occurs is determined.

For example, changing main jets to resolve an off-idle
hesitation or rich condition would do nothing as the main
jet’s effect on total fuel output is minimal at idle speeds.

4.5

Fuel System

4

9923396 - 2007-2012 EDGE/Widetrak LX Service Manual

©2011 Polaris Sales Inc.

Starting / Enrichment System

The starting or enrichment system provides additional fuel
required to start the engine in cold conditions. A cold
engine requires more fuel to start than a warm engine
because the fuel mixture tends to condense on the intake
and cylinder walls rather than vaporize as it would in a
engine at operating temperature.

Mikuni VM carburetors use a plunger-type starting
system. When the choke lever is engaged, a spring-
loaded plunger is pulled away from the starting circuit
orifice allowing additional fuel to be drawn out of the float
bowl along with the fuel drawn through the pilot jet system.

Because the starting system provides fuel not metered by
the pilot or main jet systems, it is important to verify the
plunger properly closes when not needed. A starting
system that is stuck open or improperly set will cause rich
running and heavy plug fouling.

Likewise, a plunger that is stuck closed or does not open
far enough will make starting a cold engine difficult.

Float System

The float system is designed to maintain a constant height
of gasoline during operation. When the fuel flowing from
the fuel pump into the float chamber through the needle
valve reaches the constant fuel level, the floats rise. When
the buoyancy of the float and the fuel pressure of the fuel
pump balance, the needle valve sticks fast to the needle
seat, preventing further delivery of gasoline, thereby
holding the standard level of gasoline.

The fuel level in the bowl assists in controlling the amount
of fuel in the fuel mixture. Too high a level allows more fuel
than necessary to leave the nozzle, enriching the mixture.
Too low a level results in a leaner mixture, since not
enough fuel leaves the nozzle. Therefore, the
predetermined fuel level should not be changed arbitrarily.

Idle Speed Adjustment

The idle speed adjustment screw sets the height of the
throttle slide inside of the mixing chamber. Turning the
screw in (clockwise) raises the throttle slide and raises
engine RPM. Turning the idle speed screw out (counter-
clockwise) lowers the throttle slide and lowers engine
RPM.

Always set the idle speed after the engine reaches
operating temperature. 

Air Screw

The air screw controls the amount of air that is mixed with
the fuel drawn out of the float bowl. The more air allowed
to mix with the fuel, the leaner the fuel mixture. Turning the
screw in (clockwise) reduces the amount of air, while
turning the screw out (counter-clockwise) increases the
amount of air.

Pilot Jet

From idling to low speeds, the fuel supply is metered by
the pilot jet. There are several air bleed openings in the
sides of the pilot jet which reduce the fuel to mist. The
number stamped on the jet is an indication of the amount
of fuel in cc's which passes through the jet during a one
minute interval under a given set of conditions.

Main Jet

When the throttle
opening becomes
greater and the area
between the needle jet
and jet needle
increases, fuel flow is
metered by the main
jet. The number on the jet indicates the amount of fuel
which will pass through it in one minute under controlled
conditions. Larger numbers give a greater flow, resulting
in a richer mixture. Main jets are screwed directly into the
needle jet base.

Jetting Guidelines

Changes in altitude and temperature affect air density,
which is essentially the amount of oxygen available for
combustion. In low elevations and cold temperatures, the
air has more oxygen. At higher elevations and in higher
temperatures, the air is less dense.

Verify the production setting for your specific model. All
carburetors must be re-calibrated if operated outside the
production temperature and/or altitude range. The main
jet installed in production is not correct for all altitudes and/
or temperatures. Refer to the jetting cart in the
Specifications Chapter of this manual for correct jetting for
altitude/temperature ranges.

NOTE:  It is the owner's responsibility to ensure that
the correct jets are installed in the machine for a
geographical area. Be very careful when jetting down
in warm weather. As the weather turns colder it will be
necessary to re-jet to prevent engine damage. When

 

 

 

 

 

 

 

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