9916575 1998-1999 Big Boss 6x6 Service Manual Chapter
Contents
1. Carburetor Supplies atmospheric pres All systems Vent lines 2 into 1 to frame sure to fuel in float chamber All throttle ranges Starter Choke Lever Cable Choke Supplies additional fuel air All throttle ranges Choke Enrichment Plunger Return Spring Carb mixture necessary for cold Greatest effect at low throttle Passages Starter Jet Starter starting settings and idle Bleed Pipe Pilot Idle System Pilot Jet Passageways Pilot Primarily supplies fuel at idle Mainly idle to 1 4 throttle Mixture Screw with Spring and low throttle settings Minimal effect after 1 2 Washer and Sealing O Ring throttle Bypass Ports Behind Throttle Plate Pilot Air Jet Pilot Outlet Throttle Plate Main System Main Jet Main Air Jet Main Supplies fuel at mid range 1 4 to full throttle Air Passage Needle Jet Jet and high throttle settings Needle Vacuum Slide Throttle Plate VENT SYSTEMS CV CARBURETOR The carburetor float bowl vent lines supply atmospheric pressure to the fuel in the float bowl The lines must be To frame free of kinks and restrictions and be properly routed to al To frame low fuel to flow in the proper amount and to prevent con taminants from entering the carburetor So POLARIS 4 5 FUEL SYSTEM CARBURETION MIKUNI CV CARB OPERATION The constant velocity carburetor incorporates a mechanically operated throttle plate and a vacuum controlled slide valve vacuum slide The venturi cross section2. ee Pressure Slide V a A f 1g VA LA H KA H 4 sl MA From heed Air Box Zz YA Ep ing NN EG WG SI a a P HI SSS SSS ASS NS aa ne ji te LS em PD g 6 Let lij SEI IG yu elt Venturi Stee Air Flow am Ai Flow Gomi Low Pressure s Low Pressure Note Diagrams are for explanation of theory only and are not true representations of Mikuni BST 34 carburetor FUEL SYSTEM CARBURETION PILOT IDLE AND SLOW SYSTEM This system supplies fuel during engine operation with throttle valve closed 1 or slightly opened The fuel from float cham ber 2 is metered by pilot jet 3 where it mixes with air coming in through pilot air jet 4 The mixture then goes up through pilot passage to pilot screw 5 A part of the mixture is discharged into the main bore out of bypass ports 6 The remain der is then metered by pilot screw and dis charged into the main bore through pilot outlet 7 STARTER SYSTEM CHOKE OR ENRICHMENT When the choke cable 1 is activated the starter plunger 5 is lifted off the seat Fuel is drawn into the starter circuit from the float chamber 2 through the starter jet 3 Starter jet meters this fuel which then flows into starter pipe 4 and mixes with the air 7 coming from the float chamber The mixture rich in fuel con tent reaches starter plunger and mixes again with the air coming through a pas sage 8 extending fro
3. spring e Jet needle position incorrect e Incorrect pilot screw adjustment Rich Mixture Symptoms Fouls spark plugs black sooty exhaust smoke rough idle poor fuel economy engine runs rough misses poor performance bog engine loads up backfire e hir intake restricted inspect intake duct e Air filter dirty plugged e Choke plunger sticking incorrectly adjusted choke e Choke cable binding or improperly routed e Incorrect pilot air fuel screw adjustment e Faulty inlet needle and seat e Faulty inlet needle seat O Ring e Float level too high e Poor fuel quality old fuel e Loose jets e Worn jet needle needle jet or other carburetor parts e Dirty carburetor air bleed passages or jets e Weak or damaged vacuum piston return spring e Fouled spark plug Poor Idle Symptoms Idle too high e Idle adjusted improperly idle mixture screw damaged e Sticky vacuum slide e Throttle cable sticking improperly adjusted routed incorrectly e Choke cable sticking improperly adjusted routed incorrectly FUEL SYSTEM CARBURETION TROUBLESHOOTING CONT Idle Too Low e Choke cable bending or incorrectly adjusted e Idle speed set incorrectly e Idle mixture screw misadjusted or damaged e Belt dragging e Ignition timing incorrect e Worn jet needle needle jet Erratic Idle e Choke cable bending or incorrectly adjusted e Throttle cable incorrectly adjusted e Air leaks dirty carburetor passages pilot circuit e Pilot mixture screw damage
4. the jets if they are extremely dirty or have a buildup of fuel residue or bacterial growth Even a small amount of residue will reduce the flow characteristics of the jet 4 Verify all passages and jets are unobstructed by spraying electrical contact cleaner through the passages CAUTION Do not use wire or welding tip cleaners on the jets as the orifice size may be altered 5 Use low pressure air to dry carburetor body and all components FUEL SYSTEM CARBURETION CARBURETOR INSPECTION 1 Inspect jet needle and needle jet for wear Look for discoloration shiny spots or and area that looks different than the rest of the needle The middle to upper portion of the needle where it contacts the o needle jet is the most likely wear point If jet needle shows signs of wear replace both needle and needle jet to prevent a rich condition de this 2 Inspect the inlet needle tapered surface for any sign of wear or damage Be sure the spring loaded pin is free moving and returns freely when pushed The inlet Good Condition Worn Deposits needle and seat should be pressure tested after assembly Wear areas Needle FUEL SYSTEM CARBURETION CARBURETOR ASSEMBLY 1 Inspect the diaphragm A for holes deterioration or damage Make sure the diaphragm is pliable but not swollen The diaphragm should fit properly in the carburetor body Replace diaphragm assembly if diaphragm is damaged 2 Replace parts in proper order The
5. 1 mm 3 If adjustment is necessary bend the tongue slightly 5 Float arms even Be sure float arms are even on left and right side Bend to adjust float FUEL SYSTEM CARBURETION NEEDLE AND SEAT LEAKAGE TEST 1 Install the float bowl Invert the carburetor and install a Mity Vac PN 2870975 to the fuel inlet fitting Apply 5 PSI pressure to inlet fitting The needle and seat should hold pressure indefinitely If not inspect needle and seat and seat O ring Mity Vac PN 2870975 FUEL LEVEL A fuel level test can be performed on some models if the drain hose fitting is accessible Be sure to re attach the bowl drain hose after performing the test A fuel level test allows you to observe the height of the fuel in the float bowl without removing the carburetor The fuel level can be ob served with the engine either running or shut off however engine must run briefly to allow fuel level to stabilize 1 Attach a clear line to drain fitting Be sure line fits tightly on fitting Position hose along side of carburetor as shown 7 Bowl Mating 2 Open bowl drain screw by turning counterclockwise sme approximately two turns Start and run engine for 3to 5 seconds to allow fuel level to stabilize in the line Iflevel is out of specification remove carburetor and inspect inlet needle and seat float height passages etc 3 Ifaline was removed to perform this procedure it must be replaced FUEL SYSTEM CA
6. CHAPTER 4 FUEL SYSTEM CARBURETION Jetting Guidelines 4 1 Main Jet Selection 4 1 Fuel Tank Asm Exploded View 4 2 Fuel Flow Diagram 4 3 Main Jet Pilot Jet Part Numbers 4 4 CV Carburetor System Function 4 Cycle 4 5 CV Carburetor Vent System 4 Cycle 4 5 CV Carburetor Operation 4 6 4 8 Exploded View Mikuni BST 34 Carburetor 4 9 Disassembly Notes CV Carburetor 4 10 4 11 Cleaning CV Carburetor 4 11 Inspection CV Carburetor 4 12 Assembly CV Carburetor 4 13 Adjustment CV Carburetor 4 14 4 15 Fuel Pump Disassembly Inspection Assembly 4 16 Fuel Pump Exploded View 4 17 Troubleshooting 4 18 4 19 FUEL SYSTEM CARBURETION 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 In higher elevations and higher temperatures the air is less dense Carburetors are calibrated for an altitude of 0 3000 ft 0 900 meters and ambient temperatures between 440 and 480 F 5 to 26 C Carburetors must be re calibrated if operated outside the production temperat
7. RBURETION FUEL PUMP The Polaris 6x6 is equipped with a pressure regulated fuel pump about 1 3 PSI The pump is located under the headlight cover at the front of the machine Refer to illustration on following page for fuel pump component identification To test the fuel pump 1 2 3 4 Turn fuel off Disconnect impulse line from pump Connect Mity Vac PN 2870975 to the impulse line fitting on the pump Apply 5 inches Hg vacuum to the pump fitting The diaphragm should hold vacuum indefinitely If fuel is present in the impulse line or vacuum chamber of the pump the diaphragm is ruptured and the pump diaphragms must be replaced FUEL PUMP DISASSEMBLY Pon gt Refer to illustration on following Remove the screws from the pump diaphragm cover Note the location of the two longer screws Remove the diaphragm cover gasket diaphragm and valve body gasket Remove the outlet check valve cover diaphragm and gasket FUEL PUMP INSPECTION ASSEMBLY Inspect inlet and outlet check valves for cracks warpage or damage Inspect the diaphragms for cracks holes or swelling To clean the valves or pump body remove the set screw and washer Remove the valve and wash with soap and water Carburetor cleaner may be used to clean the pump body when the check valves are removed CAUTION Some carburetor cleaners are very caustic and should not be used to clean the non metal parts of the fuel pump Check the sealing sur
8. al area in the carburetor bore is increased or decreased automatically by the vacuum slide which moves according to the amount of negative pressure less than atmo spheric present in the venturi A diaphragm attached to the top of the vacuum slide is sealed to the slide and to the carburetor body forming two chambers The chamber above the diaphragm is connected to the venturi area by a drilled orifice in the center of the vacuum slide The chamber below the diaphragm is vented to atmospheric pressure by a passage on the air box side of the carburetor A spring installed in the center of the vacuum slide dampens the slide movement and assists the return of the slide When the throttle plate is opened and engine speed begins to increase the pressure in the venturi and therefore in the chamber above the diaphragm becomes significantly lower than atmospheric Atmospheric pressure in the chamber below the diaphragm forces the diaphragm upward raising the slide against spring pressure When the pressure above and below the diaphragm are nearly egual the slide moves downward under spring pressure Raising or lowering the slide increases or decreases the cross sectional area in the venturi and therefore the air velocity in the venturi is kept relatively constant This provides improved fuel atomization and optimum fuel air ratio Low Pressure Low Pressure Diaphragm From Venturi Diaphragm Pare From Venturi Air Box eee Vacuum
9. d or adjusted incorrectly e Tight valves e Ignition timing incorrect e Belt dragging e Dirty air cleaner e Engine worn e Spark plug fouled e Idle speed set incorrectly speed limiter e Worn jet needle needle jet
10. esult Do not smoke or allow open flames or sparks in or near the area where refueling is performed or where gasoline is stored If you get gasoline in your eyes or if you should swallow gasoline see your doctor immediately Ifyou spill gasoline on your skin or clothing immediately wash it off with soap and water and change clothing gt gt BB BBB FUEL SYSTEM CARBURETION FUEL TANK ASSEMBLY Fuel tank mounted valve FUEL SYSTEM CARBURETION FUEL FLOW DIAGRAM Fuel Tank Vent Fuel Tank Fitting Screens Carburetor Vent Fuel Valve Located Above Oil Tank FUEL SYSTEM CARBURETION MIKUNI JET PART NUMBERS Main Jet Part Numbers Mikuni BST Carburetor Jet Number Part Number 112 5 3130554 115 3130555 117 5 3130556 120 3130557 122 5 3130558 125 3130559 127 5 3130560 130 3130561 132 5 3130562 135 3130563 137 5 3130564 140 3130527 142 5 3130566 145 3130567 147 5 3130568 150 3130569 152 5 3130570 155 3130571 157 5 3130572 160 3131141 162 5 3131142 165 3131143 167 5 3131144 170 3131145 Pilot Jet Part Numbers Mikuni BST Carburetor Jet Number Part Number 40 0 3130624 42 5 3130526 FUEL SYSTEM CARBURETION CV CARBURETOR SYSTEM FUNCTION Carburetor Component Function Float System Inlet Pipe Needle and Seat Maintains specified fuel level All systems Fuel Level Control Float Float Pin in float chamber carburetor All throttle ranges float bowl Venting Vent Passages in
11. faces of the pump body and covers Carefully remove all traces of old gasket and check the surfaces for damage Replace diaphragms and gaskets as a set Reassemble the pump in the reverse order of disassembly Tighten all screws evenly 4 16 Gp POLARIS FUEL SYSTEM CARBURETION FUEL PUMP EXPLODED VIEW 4 Born 5 Ab Gp POLARIS OO 6 pag A OY PNDNAGN Fuel Pump Assembly Diaphragm Gasket Set Screw and Washer Assembly Screw and Washer Assembly Screw and Washer Assembly Pressure Regulator Fuel Inlet Fuel Outlet 4 17 FUEL SYSTEM CARBURETION TROUBLESHOOTING Fuel Starvation Lean Mixture Symptoms Hard start or no start bog backfire popping through intake exhaust hesitation detonation low power spark plug erosion engine runs hot surging high idle idle speed erratic e No fuel in tank e Restricted tank vent or routed improperly e Fuel lines or fuel valve restricted e Fuel filter plugged e Carburetor vent line s restricted e Plugged or restricted inlet needle and seat screen or inlet passage e Clogged jets or passages e Float stuck holding inlet needle closed or inlet needle stuck e Float level too low e Fuel pump inoperative e Air leak at impulse line e Restricted impulse line kinked pinched e Intake air leak throttle shaft intake ducts airbox or air cleaner cover e Ruptured vacuum slide diaphragm Vacuum slide stuck closed or sticky e Improper
12. m underneath the diaphragm The rich fuel air mixture for starting is discharged through starter out let 6 in the the main bore FUEL SYSTEM CARBURETION FLOAT SYSTEM Fuel enters the float chamber 3 by means of the inlet pipe and passage through a screen on the back of the inlet needle seat 4 and around the inlet needle 2 As the fuel fills the float cham ber the float 1 rises and forces the inlet needle against the seat shutting off the orifice in the seat When fuel level is up in float chamber floats are up and needle valve remains pushed up against valve seat Under this condition no fuel enters the float chamber As the fuel level falls floats go down and needle valve unseats itself to admit fuel into the chamber In this manner the needle valve admits and shuts off fuel alternately to maintain a practically constant fuel level inside the float chamber MAIN SYSTEM As throttle valve 1 is opened engine speed rises and this increases negative pressure in the venturi Consequently the vacuum slide 2 moves upward The fuel in float chamber 3 is metered by main jet 4 and the metered fuel enters needle jet 5 in which it mixes with the air admitted through main air jet 6 to form an emul sion The emulsified fuel then passes through the clearance between needle jet 5 and jet needle 7 and is discharged into the venturi A Mixture proportioning is accompli
13. shed in needle jet 5 the clear ance through which the emulsified fuel must flow is determined ultimately by throttle position and vacuum slide height FUEL SYSTEM CARBURETION BST 34 CARBURETOR EXPLODED VIEW Carburetor Assembly Screw Throttle Valve Cover Diaphragm Jet Block Assembly Spring Diaphragm Assembly Ring 9 E Ring 10 Ring 11 Needle Jet 12 Cover 13 0 Ring 14 Throttle Shaft Assembly 15 Ring 16 Seal 17 Spring 18 Packing 19 E Ring 20 Cap 21 Screw 22 Drain Screw 23 0 Ring 24 Washer 25 Adjuster 26 Spring 27 Pilot Jet 28 Main Jet 29 Washer 30 Jet Needle 31 Float Assembly 32 Float Body Assembly 33 Float Pin 34 Needle Valve 35 0 Ring 36 0 Ring 37 Filter 38 Screw 39 Screw 40 Screw 41 Guide Holder 42 Spring 43 Plunger Assembly 44 Spring Washer 45 Screw 46 Air Jet 47 Cable Guide Jet Needle 48 Spring Refer to Page 4 4 for Jet Part Numbers E Clip Position 49 Ring 50 Adjust Screw 51 Screw and Washer Assy ON DO AR WN FUEL SYSTEM CARBURETION CARBURETOR DISASSEMBLY MIKUNI CV Use the following disassembly assembly and inspection techniques to service a CV carburetor 1 Remove carburetor diaphragm chamber cover with aratchet style screwdriver DO NOT use an impact driver to remove the screws or carburetor may be permanently damaged 2 Use a small spring loaded center punch to remove pressed float pin NOTE Set the center punch to the sof
14. spring seat washer B is stepped and must be placed on TOP of E Clip C Spacer washer D must be installed below the E Clip Refer to parts manual for more information 3 Be sure the tab E on outer edge of diaphragm is positioned properly in the carburetor body 4 Install the pilot mixture screw spring washer and O ring as an assembly Lubricate the O Ring with oil or light grease before installation CAUTION Do not damage the O ring during installation Turn the screw in until it lightly contacts the seat Back out the specified number of turns NOTE The final pilot idle mixture must be adjusted with the engine running Refer to Page 2 13 Pilot Mixture Screw Base Setting Turns Out Refer to General Specifications Pilot Screw Chapter 1 FUEL SYSTEM CARBURETION FLOAT HEIGHT ADJUSTMENT 1 Place the carburetor on a level surface as shown at right to remove weight from float arm In this position the float tongue will rest lightly on the inlet needle valve pin without compressing the spring 2 Measure the height from the float bowl mating surface to the top of step in float as shown Both sides of float should be parallel to each other The measurement should be made at the mid point on the top of the float using float adjustment tool PN 2872314 or a vernier caliper When measuring the height be sure the inlet needle valve spring is not compressed Float Height Std BST 34 14 7mm 58
15. test setting if adjust able to avoid damage to float pin tower 3 Remove inlet needle seat retaining screw along with plate and carefully remove needle seat NOTE Do not use a pliers to remove the seat or permanent damage may occur 4 10 Gp POLARIS FUEL SYSTEM CARBURETION CARBURETOR DISASSEMBLY MIKUNI CV CONT 4 Do not misplace the pilot mixture screw spring flat washer or O Ring If anti tamper plug is installed in pilot screw cavity refer to Maintenance chapter 2 for removal procedure 5 NOTE The starter jet is not removeable Starter Jet CARBURETOR CLEANING 1 Thoroughly clean the carburetor body jets and all passages with carburetor cleaner or electrical contact cleaner Protect eyes from contact with cleaner If you get cleaner in your eyes or if you swallow cleaner see your doctor immediately Some carburetor cleaners are extremely caustic and extended periods of soaking can loosen the adhesive sealer on the passage drill way plugs Do not soak rubber or plastic components such as the vacuum slide diaphragm needle seat screen or O Rings in caustic cleaning solutions Irreparable damage may occur Do not use agitator type carburetor cleaning equipment Rubber parts must be cleaned with mild detergent and hot water only 2 Ifthe carburetor is extremely dirty or contaminated with fuel residue and varnish soak for short periods only in carburetor cleaner and rinse in hot water 3 Replace
16. ure and or altitude range The main jet installed in production is not correct for all altitudes and or temperatures In addition air screw pilot screw adjustments may be required to suit operating conditions CAUTION A main jet that is too small will cause a lean operating condition and may cause serious engine damage Select the correct main jet carefully for elevation and temperature according to the charts in the General Specifications Chapter or in the Owner s Safety and Maintenance Manual for each particular model MAIN JET SELECTION IMPORTANT The following guidelines must be followed when establishing a main jet setting Select the lowest anticipated temperature at which the machine will be operated Determine the lowest approximate altitude at which the machine will be operated Select the correct main jet from the chart Clutching changes may also be required for changes in elevation Refer to clutching charts in General Specifications Chapter 1 for recommendations Gasoline is extremely flammable and explosive under certain conditions RO Ns Always stop the engine and refuel outdoors or in a well ventilated area Do not overfill the tank Do not fill the tank neck Never start the engine or let it run in an enclosed area Gasoline powered engine exhaust fumes are poison ous and can cause loss of consciousness and death in a short time Never drain the float bowl when the engine is hot Severe burns may r
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