Carburetor

DESCRIPTION

The Keihin carburetor is a horizontal, gravity fed type with a float operated inlet valve, an accelerating pump, a throttle stop screw for low idle speed adjustment, and choke system with a high idle speed adjustment.

The high idle speed cam operates in conjunction with the choke to progressively raise the idle speed as the choke disc closes.

CAUTION — This carburetor has been designed to control exhaust emissions. Any carburetor modifications or adjustments other than specified in this section may be in violation of Federal or state regulations.

Figure 3-47. Carburetor -1980 and Later

FROM FUEL TANK

21. Inlet valve

23. Float

29. Float chamber

FROM FUEL TANK

Mid-Range System (Figure 3-50)

As the throttle valve opens, the edge of the throttle valve passes the mid-range port. Fuel in the bypass passage is drawn by negative pressure in the venturi, metered by the mid-range jet and discharged into the venturi from the mid-range port.

High Speed (Main Metering) System (Figure 3-49)

The main metering system functions when the throttle valve opens past the mid-range system. The fuel metered by the

Rapid throttle action pushes pump rod (7) down, flexing diaphragm (31). This flexing action forces fuel past a check valve into the venturi. The check valve prevents backflow during this stroke. A spring then returns diaphragm to its

VENTURI

CHOKE VALVE

MAIN

Bypass Hole Carburetor Yamaha Ss125

IDLE PORT BYPASS

THROTTLE VALVE

MAIN JET BLEED TUBE

BLEED TUBE

MAIN JET AIR PASSAGE

VENTURI

MAIN JET BLEED TUBE

BLEED TUBE

9. Limiter cap (1978 to 1979 models only) 12. Low speed mixture screw

25. Low speed jet

26. Main jet

CHOKE VALVE

LOW SPEED JET AIR PASSAGE

IDLE PORT BYPASS

THROTTLE VALVE

MAIN

MAIN JET AIR PASSAGE

Figure 3-51. Accelerating System original position and a new supply of fuel flows in under diaphgram for the next acceleration.

Figure 3-49. Carburetor Low Speed and Main System

Figure 3-50. Mid-Range System main jet (26) enters the bleed tube portion of the main nozzle where it mixes with air from the main jet air passage. This fuel/air mixture is then discharged into the venturi from the main nozzle.

CHOKE SYSTEM (Figure 3-46)

The choke system is composed of a choke plate (41) and a high idle cam (48). The choke is manually set by pulling choke button out. By adjusting choke button, choke valve and high idle cam can be positioned either completely closed (fully choked for cold engine), partially open, fully open with fast idle, or fully open (off for warm engine).

The high idle cam increases engine idle speed progressively as the choke knob is pulled out. The choke knob has four operating positions. In the first position (choke knob all the way in), the choke plate is fully open and engine operates at low idle speed setting controlled by throttle stop screw (10). When choke knob is pulled out to first detent, choke plate remains fully open and high idle cam (48) moves throttle valve to high idle position. This setting is controlled by screw (3). At the second detent, choke plate is half-closed and throttle plate opens more. With the choke button pulled all the way out, choke plate is fully closed for cold engine starting.

The choke plate is spring loaded to permit the engine to continue to run after cold starting without the need to push the choke knob in until the engine begins to warm up.

Location Baffles Plate Carburetor

Figure 3-50. Mid-Range System

ACCELERATING SYSTEM (Figure 3-51)

The accelerating pump system uses sudden throttle openings (rapid accelerations) to quickly inject fuel into carburetor to provide extra fuel for smooth acceleration.

Carburetor Adjustment (Figure 3-46, 3-47)

CAUTION — Carburetor modifications or adjustments other than specified in this section may be in violation of Federal or state regulations.

VENTURI

PUMP NOZZLE

CHECK VALVE

PUMP LEVER

THROTTLE SHAFT

FUEL

FUEL

7. Pump rod 31. Diaphragm

SPRING

VENTURI

PUMP LEVER

THROTTLE SHAFT

PUMP NOZZLE

CHECK VALVE

The carburetor has been adjusted at the factory for maximum performance and minimum emissions of hydrocarbons and carbon monoxide.

Low Speed Mixture Adjustment (1979 and Earlier)

NOTE: On 1980 and later models, the low speed mixture is set at the factory and sealed.

In normal service, the low speed mixture limiter cap (9) should not be removed. Low speed mixture may be adjusted within the limited range of the cap if necessary.

If the limiter cap has been removed and low speed mixture altered, proceed as follows:

Carefully turn low speed mixture screw (12) all the way in, clockwise, until just seated. Do not overtighten. Back screw out to specification found in figure 3-52. With screw in this position, install limiter cap (9) in central position on adjusting screw.

With the engine warm and the choke off, adjust the throttle stop screw (10) so that engine idles at 900 rpm. Turn the limiter cap (9) clockwise for a richer mixture, counterclockwise for a leaner mixture. The mixture should be adjusted to the leanest setting that results in a smooth idle.

Recheck slow idle speed setting and readjust to 900 rpm if necessary.

Model

Carburetor Part No.

Turns Open

FX-1200

27468-78

1-1/8

FLH-1200

27467-78

1-1/8

FLH-80

27466-78

3/4

Figure 3-52. Low Speed Mixture Screw Setting

Figure 3-52. Low Speed Mixture Screw Setting

Slow and Fast Idle Speed Adjustments (Figure 3-46, 3-47)

With engine at normal operating temperature and choke in fully open position (choke knob all the way in) adjust throttle stop screw (10) so that engine idles at 900 rpm. Pull chole knob out to first detent position (choke plate fully open, fast idle cam contacting throttle shaft lever). Turn screw (3) in or out, as required to set engine fast idle at 1500 rpm. With choke knob all the way in, recheck slow idle speed.

DISASSEMBLING CARBURETOR (Figure 3-53) WARNING

Gasoline is extremely flammable and highly explosive under certain conditions. Do not smoke or allow open flame or sparks when refueling or servicing the fuel system.

Remove air cleaner assembly.

Turn off gas tank valve and disconnect fuel line at carburetor. Disconnect throttle wire and choke wire from their respective levers. Remove carburetor from engine by removing nuts and washers on mounting studs. Note position of gaskets.

Disassemble accelerating pump as follows: Remove accelerating pump housing by removing three sets of screws and washers (34 and 35). Remove spring (32), diaphragm (31) and O-ring (30), taking care when lifting off housing (33) to catch spring (32). Be careful not to damage housing gasket surface to prevent fuel leakage when reassembling.

Disassemble float chamber as follows: Detach float chamber (29) from body by removing three sets of screws and washers (34). Remove screw (6) which retains float pin (5) and remove float (23). Slip inlet valve (21) off metal clip on float. If needed, remove clip (22) from inlet valve (21). Take care not to damage rubber needle portion of inlet valve. Be careful not to damage pump nozzle and overflow pipe which are built into the float chamber. Remove gasket (28) from slot in float chamber wall.

The removal of the float chamber will allow pump rod (7) and boot (8) to be removed.

Disassemble carburetor body as follows: Pull plug (27) out of tube above low speed jet (25). Unscrew low speed jet (25) and main jet (26).

Remove nut (19) and washer (18). Pull throttle lever (17) and spring (16) off throttle shaft.

Remove limiter cap (9). Remove throttle stop screw (10) and low speed mixture screw (12) along with associated springs (11) and (13), respectively. Remove washer (40) and O-ring (39).

As required, remove brackets (2) and (15) by removing screws and washers (1) and (14).

The throttle valve assembly (shaft, valve, plate and associated parts) usually are not disassembled. These parts are matched to the individual carburetor during manufacture. In both cases, screws securing plates to shafts have peened ends, the threads of which would be destroyed if screws are removed. The bypass hole was positioned precisely to match lip of valve and wowld be changed if taken apart and reassembled. If problems arise involving these assemblies, the complete carburetor is usually replaced.

This completes disassembly of carburetor. Clean and inspect before reassembling.

CLEANING AND INSPECTING

CAUTION

Never scrape carbon deposits from carburetor parts with knife or other steel instrument. Also, do not use wires or drills to clean small holes. To do so may cause burrs or change hole sizes. This is particularly important to observe when cleaning jet openings.

Figure 3-53. Carburetor — Exploded View

/Li4

/Li4

1.

Screw and washer

28.

Gasket

2.

Bracket

29.

Float bowl

3.

High idle adjusting screw

30.

O-ring (2)

4.

Screw

31.

Diaphragm

5.

Float pin

32.

Spring

6.

Screw

33.

Housing

7.

Rod

34.

Screw and washer (5)

8.

Boot

35.

Screw and washer

9.

Limiter cap *

36.

Clip

10.

Throttle stop screw

37.

Hose

11.

Spring

38.

Fitting

12.

Low speed mixture screw*

39.

O-ring *

13.

Spring*

40.

Washer*

14.

Screw and washer

41.

Choke plate (not shown)

15.

Bracket

42.

Choke lever shaft

16.

Spring

43.

Mounting flange

17.

Throttle lever

44.

Accelerating pump lever

18.

Washer

45.

Rocker arm

19.

Nut

46.

Rocker arm spring

20.

Insulator block

47.

Intermediate lever

21.

Inlet valve

48.

High idle cam

22.

Clip

49.

Stud

23.

Float assembly

50.

Nut and washer

24.

Screw and nut

51.

Intake manifold

25.

Low speed jet

52.

Seal

26.

Main jet

53.

Clamp

27.

Plug

*

1979 and earlier

Clean carburetor body In solvent such as "GUNK" to remove varnish and carbon stains from fuel and air passages. Blow body dry with compressed air. Reverse air flow through each passage to ensure removal of all dirt particles.

Inspect all parts and replace any that are damaged or worn. The most important checks are as follows.

Check accelerating pump. Inspect diaphragm (31) for pinholes, cracks or deformation and replace if necessary. Inspect rod (7) for bending and boot (8) for cracks. Any dirt in accelerating pump passage should be blown out from side opposite nozzle or check valve will close making cleaning impossible.

Check for dirt clogging overflow hose (37). If clogged, fuel may not flow out and instead flood engine, causing poor starting.

Check low speed mixture screw (12) (1979 and earlier). Inspect for carbon lodging on tip and for damage to taper or screw, itself.

ASSEMBLING CARBURETOR (Figure 3-53)

Assembling the carburetor is essentially the reverse of disassembly with the following exceptions:

Figure 3-54. Carburetor Float Setting

Figure 3-54. Carburetor Float Setting

When assembling the carburetor, use new gaskets and firings. Check and adjust, if necessary, float level as shown in figure 3-54, using Float Level Gage, Part No. 94752-77. The adjustment is made by carefully bending the metal tab on the float. Check float level while holding carburetor so the float is in a vertical position as shown in Figure 3-54.

INSTALLING CARBURETOR ON MOTORCYCLE

Position insulator block (20, figure 3-53) and carburetor on mounting studs. Secure with nuts and washers (50). Tighten nuts to 19 ft-lbs torque.

Insert throttle wire through slot in bracket (15) and place throttle wire and ferrule end in hole in throttle lever (17). Make sure wire is seated in groove in throttle lever.

Check operation by twisting throttle control on handlebar. Throttle should open and close fully with handlebar grip movement.

With choke lever in the fully open position, attach choke wire to lever. Check operation of choke knob and lever.

Attach fuel line from-gas tank to carburetor inlet. Position overflow tube (37) downward so any fuel overflow will drip away from hot engine. Open fuel valve and check for fuel leakage.

Adjust carburetor as described under "ADJUSTING CARBURETOR."

Install air cleaner as described under "AIR CLEANER."

KEIHIN CARBURETOR TROUBLE CHART

Overflow

Check for:

Remedy:

1. Worn fuel valve (21) or dirty fuel valve seat.

2. Improper fuel level in float chamber (29).

3. Worn float (23) mounting tabs.

5. Damaged float chamber gasket (28).

6. Loose float chamber screws (34).

7. Deformed float (23).

1. Replace valve (21 ) or clean valve seat.

2. Adjust float (29) mounting tabs for correct fuel level.

7. Replace float (23).

Poor Idling

Check for:

Remedy:

1. Idling improperly adjusted.

2. Damaged low speed mixture screw (12).

3. Clogged bypass or idle port.

4. Clogged low speed jet (25).

6. Air leaking into system.

7. Excessive fuel from accelerating pump.

1. a. Adjust fast and slow idle speeds.

b. Adjust low speed idle mixture screw limiter cap to full rich or full lean limit. (1979 and earlier)

2. Replace screw (12). (1979 and earlier)

6. Replace insulator block (20) and tighten screws.

7. Check accelerating pump rod (7) length.

Poor Fuel Economy

Check for:

1. Fuel level too high.

2. Clogged bleed tubes.

3. Loose jets.

4. Idling improperly adjusted.

5. Choke not opening fully.

1. Adjust level of float (23).

3. Tighten.

4A. Adjust fast and slow idle speeds. B. Adjust low speed mixture cap within its limits (1979 and earlier).

5. Inspect choke and choke wire and adjust or replace.

6. Clean.

Poor Acceleration

Check for:

Remedy:

1. Clogged accelerating system.

2. Damaged accelerating pump diaphragm (31).

3. Low speed system improperly adjusted.

4. Clogged low speed jet (25) or bleed tube.

2. Replace diaphragm (31).

3. Adjust low speed system (1979 and earlier).

5. Adjust level of float (23).

Hard Starting

Check for:

Remedy:

1. Choke plate (41) not operating properly.

2. Generally dirty carburetor.

3. Loose carburetor mounting nuts.

4. Fuel overflow.

1. Adjust choke system.

2. Disassemble and clean.

3. Tighten mounting nuts.

4. Inspect float (23) and fuel valve (21) and adjust or replace.

KfclHIN CARBURETOR TROUBLE CHART (CONT)

Poor Performance On Road

Check for:

Remedy:

1. Idling improperly adjusted.

2. Fuel overflow.

4. Air leak in intake system.

5. Faulty operation of accelerating pump.

6. Dirty or clogged carburetor or air cleaner.

1. Adjust idle.

2. Inspect float (23) and fuel valve (21) and adjust or replace.

3. Inspect main jet (26) and tighten.

4. Check air cleaner backing plate and manifold mounting.

6. Clean.

Poor High Speed Performance

Check for:

Remedy:

2. Improper fuel level in float chamber (29).

3. Dirt lodged in strainer in fuel tank.

4. Clogged main jet (26) or main jet air passage.

1. Inspect main jet and tighten.

2. Adjust float (23) mounting tabs for correct fuel level.

3. Clean strainer.

4. Clean.

Abnormal Combustion (Fuel Mixture)

Check for:

Remedy:

1. Generally dirty carburetor.

2. Dirty or clogged fuel line.

3. Air leaking into system.

1. Disassemble and clean.

2. Clean fuel line or replace.

3. Check mounting nuts for tightness or replace insulator block (20).

Loss of Power (Fuel Insufficient)

Check for:

Remedy:

1. Clogged fuel line.

2. Dirty fuel tank.

3. Air leaking into system.

4. Accelerating pump not working.

5. Clogged fuel strainer in fuel tank.

6. Generally dirty carburetor.

3. Check mounting nuts for tightness or replace insulator (20).

4. Repair and adjust.

5. Clean strainer.

6. Disassemble and clean.

Loss of Power (Air Insufficient)

Check for:

1. Dirty air cleaner.

2. Throttle cable not working.

3. Correct jetting for high altitude operation.

1. Clean or replace air cleaner element.

2. Check throttle cable and adjust or replace.

3. Install high altitude kit.

4. Tighten jets.

AIR CLEANER

GENERAL

The air cleaner consists of a backing plate, filter element, baffle plate and cover, arranged so all air drawn into the carburetor passes through the filter. A plastic foam element traps air borne dust to keep it from entering carburetor and engine.

Remove air cleaner cover and inspect filter element at least every 1250 miles, or more often under dusty service conditions.

SERVICING AIR CLEANER (Figure 3-55)

The carburetor air cleaner is equipped with a plastic foam element which is oil saturated. To inspect and service filter element (5), remove 3 socket head screws and washers (1 and 2). Pull air cleaner cover (3) off to release baffle plate (4) and filter element (5). The need for servicing is indicated by the appearance of the outside surface of the filter. Filter should be cleaned and re-oiled if a film of dirt has built up covering the surface pores, or if light spots show on the surface which means that dust is drying out the oil. A dirty, dark appearance is normal, as long as pores in the filter remain open and covered with an oil film.

To clean filter, remove the foam element from the wire mesh core and wash it in a non-flammable petroleum solvent or detergent and water. Allow to dry thoroughly and saturate with same weight oil as recommended for the engine crankcase. Apply oil to element liberally, working it in until element is uniform in color indicating uniform saturation. After excess oil has drained off, replace element on screen.

Before reassembling air cleaner, make sure socket head screws (7) are tightened to 75 to 85 in -lbs torque. Make sure seal strip (6) is in place. Assemble remaining parts in reverse order of disassembly.

INSTALLING AIR CLEANER (Figure 3-55)

Check backing plate (14) gasket surface to make sure it is flat. Assemble mounting brackets (13) to rocker arm covers with bolts (10) finger tight. Hold backing plate (14) in place on carburetor and move brackets (13) so they are flat against backing plate. Remove backing plate and tighten bolts (10) to 12 to 15 ft-lbs torque. If mounting brackets are not adjusted properly, the backing plate will be distorted when it is mounted and air leaks will develop at the carburetor mounting flange. Slip crankcase vent hose on backing plate fitting. Assemble gasket (12) and backing plate (14) to carburetor using socket head screws (7). Tighten screws to 75 to 85 in-lbs torque. Secure backing plate to mounting brackets using bolts and washers (9) and nuts (8). Tighten nuts to 12 to 15 ft-lbs torque.

1. Socket head screw (3)

3. Air cleaner cover

4. Baffle plate

5. Filter element

6. Seal strip

7. Socket head screw (3)

10. Bolt, lockwasher and washer (2)

11. Crankcase vent hose

12. Gasket

13. Mounting bracket (2)

14. Backing plate

Figure 3-55. Air Cleaner — Exploded View

3-44

Install seal strip (6) on backing plate. Assemble filter element (5), baffle plate (4), cover (3), screws (1) and washers (2). Tighten cover screws to 12 to 15 ft-lbs torque.

FUEL TANK

GENERAL

The fuel tanks are of welded steel construction. Fuel tanks are treated to resist rusting. However, when the motorcycle is not operated for any length of time (e.g. over winter), tanks should be drained and the tank interior bathed with an oil-fuel mixture of equal proportions. The fuel will evaporate leaving a protective oil film on tank walls.

REPAIRING LEAKING TANKS

Many tank leaks may be repaired with epoxy type materials. Follow manufacturers instructions.

Tank leaks may be arc welded, gas welded or soldered. However, only firms or persons qualified to make such repairs should be entrusted with the operation.

WARNING — If ALL traces of fuel are not purged, an open flame repair may result in a tank explosion. Extreme caution in all tank repair is recommended.

FUEL SUPPLY VALVE

The fuel supply valve is located under the fuel tank. Gasoline to carburetor is shut off when the handle is in a horizontal position. Turning the handle down to vertical position turns on the main gasoline supply; turning the handle up to the vertical position turns on the reserve supply. Valve should always be in the off position when the engine is not running.

WARNING

Always close valve when engine is not running to prevent accidentally flooding engine or surroundings with gasoline.

Location Baffles Plate Carburetor

A fuel strainer is located on top of the supply valve inside the fuel tank. When fuel flow restriction is suspected, remove hose at carburetor and open valve to the reserve position to drain fuel into a suitable container.

WARNING — Gasoline is extremely flammable and highly explosive under certain conditions. Do not smoke or allow open flame or sparks when refueling or servicing the fuel system.

Remove fitting from tank, clean or replace screen and flush tank to remove ail dirt. Before reinstalling, coat threads with Harley-Davidson Pipe Sealant with Teflon, Part No. 99630-77.

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