IH: Carburetor, Intake Manifold & Exhaust Systems


FACTORY CARBURETORS

Linkert Model M and DC Carbs (1965 and Earlier)

  • Three different carburator families were used on the K and Sportsters through 1969. Three models of the venerable Linkert Model M carbs were used on K and KH. Sportsters used various incarnations of the Linkert DC and M carbs from 1957 through 1965. 1)

The Linkert Model M

  • The model M carburetor is a plain tube carb containing a venturi and a discharge nozzle through which fuel is drawn into the air stream passing through the venture. The quantity of fuel is metered by two jets or openings (one for low speed and the other for high speed) before entering the nozzle.
  • Needle valves in the low and high speed passages allow the carburetor to be adjusted for the slightly varying and individual needs of the engine. Once the carb is adjusted, it requires little if any attention. At most, adjustments might be a few clicks or notches richer or leaner on the needles are all that should be needed to correct air/ fuel mixture for changes in weather condition. All final adjustments should be made at full operating temps. 2)
  • Features:
    • High and low speed needles
    • Low speed needle lift lever
    • Throttle lever
    • Throttle lever lock screw
    • Throttle stop
    • Bowl vent
    • Choke lever and disc
    • 1-5/16“ Venturi (27363-41) for 1954-1956 KH models3)
  • (27146-52) M53 (1952) for all Harley K models4)
  • (27146-52A) M53A1 (1952-1956) for all Harley K models replaced the M53 with: 5)
    • New intake lever and shaft (52-53) replaced again for (54-56)6)
    • New float assembly (27380-33A) replaced these two previous ones (27380-33) & (27380-52) 7)
    • New carburetor support bracket (basically an “L” bracket on the bottom of the float bowl.) 8)
  • Most K models ran a Linkert M model Carb up until around 1965.

The Linkert Model DC

  • The model DC is a plain tube carburetor. It's main air/ fuel mixture passage consists of a venturi section and discharge nozzle. A fixed jet and adjustable high speed needle valve, of limited, meter the high speed fuel supply as it is fed into the venturi section of the throttle barrel. The low speed needle valve meters the low speed fuel/ air mixture as it is fed into the throttle barrel near the throttle disc. There are no moving parts except the throttle shaft, disc and the bowl float mechanism. 9)
  • The Linkert DC found on the 1959-1965 Harley Servi-car 45 flathead was left-handed, the float was on the right side of the ones put on Sportsters and Big-twins, since Harley flatheads have the carburetor on the left side of the engine. Other than the Harley Shovelhead carb and the DC-2 on the Servi-car, all Linkert DC versions have the same carb body with the same size venture, with a one-piece casting and the difference was changing the jet size, and modifying the inlet valve. 10), found primarily on '50s and '60s Harley-Davidson Sportsters.
    • Being simple in design:
    • Choke lever assembly for 1957 models only
    • Throttle lever stop
    • Main nozzle float valve and seat
    • Idle tube assembly
    • Float bowl mounted on right side
    • Venturi
    • Discharge nozzle
    • Adjustable high and low speed nozzles, and a fixed jet.
Carb ModelHD Bike Used OnIdle BleedIdle Tube FeedFixed JetThrottle DiscTurns (high speed setting)Turns (idle speed setting)
(27155-57) was the first Sportster carburetor then replaced with (27155-57A) both introduced for 1957-1959 Sportsters 11)
DC-11957-1958 Sportster XL Early Style 12)#53 .0595#69 .0293#9 .0679A 13) 3/4” to 1-1/4“ 3/4” to 1“ 14)
DC-1L1959-1960 Sportster XL 15) #53 .0595#69 .0293#4 .06259A 16) 3/4” to 1-1/4“ 1” to 1-1/4“ 17)
DC-1M1959-1960 Sportster XL 18)#53 .0595#69 .0293#1 .0529A 19) 3/4” to 1-1/4“ 1” 20)
DC-21959-65 Servicar (smaller venturi, opposite float bowl)21)#51 .067#70 .028#20 .045212 22) 3/4“ to 1-1/4” 1“ to 1-1/4” 23)
DC-61961 Sportster XLH and XLCH 24)#53 .0595#69 .0293#4 .06259A 25)
DC-71966 Big-Twin FL and FLH (larger venturi) 26)#53 .0595#69 .0293 .0709A 27)
DC-101962 and mid-63 Sportster XLH and XLCH 28)#53 .0595#69 .0293#4 .06259A 29) 3/4“ to 1-1/4” 1“ to 1-1/4” 30)
DC-121966 Big-Twin FL and FLH
mid-1963 1964 1965 Sportster XLH and XLCH 31)
#53 .0595#69 .0293#4 .06259A 32)

Adjusting the Linkert DC

Carb Idle Speed
Adjust until engine idles and runs smoothly
  • A properly adjusted carburetor requires little re-adjustment according to the FSM. It shouldn't be necessary to change the adjuster of the low speed needle more than 1/8 turn or the high speed adjuster more than 1/4 turn richer or leaner to obtain correct mixture for a change in altitude unless there are some worn or obstructed parts to consider.33)
  • Before attempting to correct faulty engine performance through carb adjustment, eliminate all other possible causes for poor engine performance such as bad spark plugs, poor timing, mal-adjusted tappets, dirty air cleaner, leaking gaskets and poor manifold connections.34)
  • The fuel/ air mixture for low engine speed is regulated by the low speed needle only. The fuel supply for high speed is regulated by a combination of the adjustable needle and the fixed jet (which dominates the regulation of high speed fuel supply). The high speed needle provides a supplement, to a degree, of the fuel supplied by the fixed jet when it is found that slightly enrichening the mixture improves engine performance. 35)
  • Both, high speed and low speed, needles turn inward (clockwise) for leaner or outward (counterclockwise) for richer mixtures at the respective speeds for which they adjust.
    • Adjust idle (low speed): Make sure the carb control wire is adjusted so the throttle lever fully closes and opens with handlebar movement.36)
    • Turn both the high and low needles all the way in (clockwise) to a light seat position but do not close off either too tight as it may damage needle and/ or seat. 37)
    • Turn low speed needle out app. 1 1/2 turns (in this position, engine will start but low speed idle will probably be too rich).38)
    • Start the engine, let it reach operating temp, choke off (open) then correct the position of the low speed needle. Turn the low speed needle in (clockwise) 1/8 turn at a time until engine leans out and misses and is inclined to stop. Then, back low speed needle out 1/8 turn at a time (allow a few seconds in between turns to allow engine to adjust) until engine hits regularly with spark advanced, throttle closed and engine running at idle speed. Starting and all around performance will be better with low speed adjustment slightly rich, rather than lean. 39)
    • Adjust throttle lever stop screw as needed to make engine idle at proper speed with throttle fully closed. Turn screw clockwise for faster or counterclockwise for slower idle speed. Be careful not to idle engine at the slowest possible speed because an extreme low idle position will cause hard starting. Changing the idle speed with the throttle screw may also alter the low speed fuel/ air mixture so remember to go back and check that adjustment and correct if needed using the above method.40)
    • Turn high speed needle out app. 3/4 turns. Check high speed adjustment by running the motorcycle on the road at various speeds between 20 mph and max speed with spark fully advanced. Re-adjust high speed needle until optimum performance is achieved. Best all around engine performance can usually be found with the high speed needle set between 3/4 and 1 1/2 turns out (open). 41)
  • The FSM may be of little use from this point on.
    • Its trial and error now to find out what works for you. Idle speed is critical in easy starting. Low idle can make bikes difficult to start and too high is uncomfortable at stops. There is a sweet spot in there somewhere that you must find. 1200 rpm is a good speed to begin your fine tuning. 42)
    • When it's warm and it's been off for a minute. I only need to push the kicker through and it starts up. If it's been off for a bit, the first kick without retarding the mag results in a locked up kicker, feeling there is a fuel charge sitting in the combustion chamber. The idle adjustment screw can be backed out as far as I want and it doesn't change much at all. If I go too lean, it will stumble of course. If the idle adj. screw is 1/8th out from stumble as the manual suggests, I have a hard time with starting. 43)
  • The bigger picture regarding these adjustments for this the throttle plate must be: Positioned (milled notch up & facing air cleaner) and registered (even peripheral contact to throttle body at fully closed) correctly.44)
    • Removing the brass screw plug near idle mix screw exposes the idle well. On the side wall of the well you will see a hole that feeds mixture (note that I didn't say fuel) to the idle mix screw. Mixture that enters this hole is regulated by the adjuster screw, and discharged into air stream thru a hole drilled close to intake manifold. This supplies most of the idle mixture.45)
    • Then on floor of the well you will see a series of 4 tiny holes. These are the transition holes. The remainder of idle mixture comes from the 1st (one closest to manifold) transition hole as its open to low manifold pressure. The other 3 are open to the higher atmospheric pressure because they are on the other side of throttle plate at idle. That means lots of air enters the well thru the 3 hi pressure holes. All that air dilutes the fuel into a 'mixture'. Because the idle mix screw adjusts the flow of this mixture a funny thing happens as you richen it. Because the air component is so much less dense than the fuel component the mix screw is less a restriction to the air than to the fuel- its gets to a point where opening it adds more air then it does fuel. In other words it will only get so rich no matter how far you back it out. This is a DC Linkert anomaly because 4 holes spread over a very large throttle plate swing bleed a lot of air into the well on idle. Things change as soon as you begin opening throttle plate. Now the number of transition holes open to low pressure is larger and the number open to atmospheric pressure is less. ie: the air component of the mixture drops. Now the idle mix screw is controlling a more fuel laden mixture. The ratio of air to fuel continuously drops as you open the throttle until the last holes is on downstream of the plate. The mix screw will have a larger effect on low throttle running than idling. You need to set screw where you get good around town manners and then adjust the speed screw to the appropriate speed.46)
  • This is a delicate balancing act that will change as the properties of the air change: temperature, pressure (altitude or barometer), and water content (humidity). The dc is prone to this fickleness due to the large air bleed variation at different throttle plate positions.47)
  • The S&S carbs based on the DC Linkert used only two transition holes in the early years and three later on. Both show a marked improvement in weather stability.48)
  • These carbs are extremely touchy to float level at just off idle throttle positions. Problems show as spitting / coughing on one end of the spectrum to burbiling / stumbling at the other end. Many owners will report how precise you need to be with float levels to get your bike to run as a fine watch.These guys also eventually learn two things:49)
    1. Float levels will rise on their own due to the steel inlet needle wearing the brass seat away. This is a mileage thing– just like tire and chain wear (steel needle carbs only- linkert, orig earlies and orignal L's). 50)
    2. Secondly and more importantly, these carbs are very susceptible to errant low speed metering as fuel composition, barometric pressure, humidity, and air temperature vary. Trying to hit the sweet spot requires many float adjustments, idle mixture settings, idle speed settings and road tests. To do away with that wasted time and aggravation, I fit all my side bowl carbs with an externally adjustable float level. Now I can change float level on a whim.51)

Linkert DC Rebuilding

  • A gasket kit (which includes the bowl and body gaskets, seals, and an o-ring for the bowl vent tube instead of a gasket) and some carburetor cleaner is all you need to rebuild a Linkert DC carb. No special tools are required. All DC carbs use the same gaskets and seals. If needed, a larger gasket set is available, and includes the gaskets and seals, plus an assortment of small springs and screws. 52)
Carb Assembly is HD Part Number: 27155-57B53)
Model
(marked on carb)
Idle Port Hole
Drill Sizes
Model
(marked on carb)
High Speed Hole
Drill Sizes
DC-1, 1L, 1M, 10
DC-2
#70 (0.028 in)
#56 (0.0465 in)
DC-1, 1L, 1M, 10, 6, 7, 12
DC-2
#55 (0.052 in)
#70 (0.028 in)

Linkert DC Pics

Linkert DC-11 54) Linkert DC-11 55)
Linkert DC-11 56) Linkert DC-11 57)

Linkert DC Mods


Linkage modified for usage with “snap” throttle 58)

Tillotson HD Carb (1966-1971)

  • 1966-1971, Sportsters used the universally beloved Tillotson Model HD, 59)which was less sensitive to lean and tilt, and also helped power and driveability. 60)
  • The model HD is a dual-venture, diaphragm-type carburetor with an automatic economizer and accelerating pump. The fuel inlet needle is operated by a compression spring balanced lever that is controlled by the diaphragm to regulate fuel flow into the metering chamber. The amount of fuel flowing into the carb metering chamber is exactly equal to amount of fuel demand of the engine. 61)
  • This type of fuel control operates at any tilt angle and is resistant to any vibration which could cause a poor fuel/ air mixture or flooding.62)
  • The small primary venture is offset to the bottom of the large secondary venture where the main nozzle outlet protrudes from the metering chamber. The accel. pump discharges into the small venture to take advantage of the venture pressure drop that breaks up the solid stream of accelerating-pump fuel.63)
  • The accelerating unit is a positive-acting plunger type pump connected to the throttle shaft through a cam lever. The pump plunger is a spring loaded leather cup that operates in a smooth plastic cylinder drawing fuel directly from the metering chamber to provide extra fuel for acceleration.64)
  • The automatic economizer is a hydraulically operated enrichment valve controlling the main nozzle fuel mixture at very low engine speed. The valve opens an auxiliary fixed main jet as the venture air flow decreases, allowing the fuel mixture to be maintained at a full power richness. As the air flow through the carb increases, or as engine speed increases, the valve closes to prevent an over-rich mixture at intermediate speeds. 65)
  • All late 1968 Electra Glide and Sportster model carbs receive an upgrade incorporating a ball check valve in the accelerator pump passage of the plastic cover.This was to provide a positive seal against air bleeding back from the venturi into the fuel chamber. 66)
    • Air bleeding into the fuel chamber thru the accel pump passage can cause poor or erratic accel pump action, surging at cruising speeds and hesitation upon acceleration from cruise speeds, a vapor lock condition while running from high speds to cruise speeds and a tendency to stall when idled.
  • Choke/ Initial Startup: The choke is in the closed position. As the engine is cranked, the entire metering system (idle, intermediate and nozzle) is subjected to engine suction which is transmitted to the fuel chamber, via the metering channels, creating a low pressure on the fuel side of the metering diaphragm. Atmospheric pressure from the vent moves the metering diaphragm toward the inlet control lever to allow fuel to enter carb thru the needle and seat. Fuel is then forced thru the metering system out into the carburetor mixing passage and into the manifold and engine. When the engine fires up, the volume of air drawn thru the carb increases, and the spring loaded top half of the choke shutter opens to provide the additional air required by the engine, to prevent an over-rich mixture. The choke can then be moved to a half-open position for engine warm-up. During hot weather or after the engine has been run long enough to reach stable operating temperature, and then shut off for a short period of time, a small amount of fuel vapor may form in the fuel lines or in the fuel chamber of the carb. The vapor in the fuel lines will enter the fuel inlet and rise out of the fuel outlet, to be vented back into the fuel tank. The vapor that forms in the fuel chamber must escape through the metering system because there is no other vent to the fuel chamber. Starting a warm engine is most easily accomplished by placing the choke in the half closed position and starting as described. The choke helps to quickly remove the vapor out of the fuel system so that the fuel flowing through the carb and fuel line can cool the system to a normal temperature. Starting is usually easier using the choke (full choke for cold engine, half choke for warm engine). 67)
  • Idle Operation: The throttle shutter is slightly open when the engine is idling and the carb mixing passage on the engine side of the throttle shutter is exposed to engine suction, while the mixing passage between the throttle shutter and the air cleaner is at nearly atmospheric pressure. Engine suction (transmitted through the primary idle discharge port to the fuel chamber side of the metering diaphragm via the bypass chamber, idle fuel supply channel, intermediate adjustment channel, nozzle well, main fuel jet and main fuel supply channel) creates a sub atmospheric pressure in the fuel chamber. The metering diaphragm is forced upward by atmospheric pressure, moving the inlet control lever to overcome the inlet compression spring pressure, allowing fuel to enter the fuel chamber through the inlet needle and seat. Fuel flows through the main supply, main fuel jet, nozzle well, intermediate adjustment channel (where it mixes with air from the idle air-bleed) idle fuel supply channel, to the bypass chamber, where it mixes with air from the secondary idle discharge ports, and on out into the carb mixing passage through the primary idle discharge port. The mixture of well atomized fuel and air then travels through the manifold and into the engine combustion chamber. 68)
  • Acceleration: Acceleration is accomplished by the use of a positive-acting accelerator pump, actuated by a cam lever from the throttle. The pump cylinder is filled when the pump is raised to the top of it's stroke. Fuel is drawn from the fuel chamber, through the accelerating pump inlet channel, past the inlet check valve. The outlet check valve is closed to prevent air from being drawn in to the accelerating pump system. As the accelerating pump is depressed, the pressure of the fuel closes the inlet check valve, the fuel flows through the pump channels, past the outlet check valve, through the accelerating pump outlet channel and through the boost venture into the carburetor mixing passage. 69)
  • Intermediate or Cruise Operation: Fuel is delivered into the carb and as the throttle shutter opens to increase engine speed, the secondary idle discharge ports are exposed to engine suction and fuel is delivered from both the primary and secondary idle discharge ports to supply the additional fuel demand by the engine. As the throttle shutter is opened farther, the air velocity through the boost venture increases, creating a low pressure area at the nozzle outlet. Fuel flows from the fuel channel through the nozzle outlet via the nozzle well, main fuel jet, main fuel supply channel, and economizer valve when the pressure at the nozzle outlet is less than the pressure in the fuel chamber. At idle and lower intermediate speeds, the check ball in the economizer valve is away from the seat, allowing free flow from the fuel chamber through the economizer valve to the nozzle well and nozzle outlet. Fuel flow from the primary and secondary idle ports decreases as fuel flow from the nozzle outlet increases. 70)
  • High Speed Operation: Fuel flow from the nozzle outlet increases as the shutter is opened past the intermediate position to the fully open position. Fuel is delivered through the nozzle outlet from the fuel chamber via the main fuel supply channel and the main fuel jet. The increased pressure difference between the small venture and the metering chamber, plus the force of fuel flowing through the economizer valve, causes the check ball to seat, stopping the fuel flow from this part of the main metering system. This gives increased economy at high speeds. The diaphragm action and the method of fuel delivery to the fuel chamber is the same as previously described. 71)
  • Features: 72)
    • Low speed needle
    • Intermediate needle
    • Throttle lever
    • Throttle stop
    • Choke lever
    • Accelerator pump
    • Inlet and vent fittings
    • Diaphragm
    • Intake Manifold (27021-57) 73)
HD-1A was the 66 version, no pump check ball, used the no drill insulator and the “wraparound” cable bracket is the same as the 67-71. 66 uses the Linkert bracket 74)
Fuel pressure and the weight of the needle alone move the needle away from the inlet seat. 75)
HD-1B Starting after engine #66XLCH-10611, the carb has a new inlet valve lever, needle and seat assembly to help correct problems such as high speed leaning out caused by vibration and needle sticking due to dirt / debris in carburetor. The stamped ID has the model stamped on the flange near the idle mixture adjustment wheel.
The new lever had a forked end which engaged a groove in the new inlet needle seat stem which locked the lever to the needle providing diaphragm control of the needle movement in both directions.
It was recommended to install this update into the HD-1A carb (where definite carburetor problems exist) 76)
67-E68 used the 'standard' choke and throttle shafts, no pump check, insulator gets drilled for over the top. Same pn. This insulator gets used on e67CH, 70-71CH and 67-71 XLH.
67-69 CH gets its own insulator. New pn for this one. Same part as others, this vintage except the lower stud is now longer for the plug wire router to mount.77)
HD-1BC or HD-1C Late 1968 Sportsters ( Carb # 27162-66B) received a ball check valve in the accelerating pump passage of the plastic cover which provides a seal against air bleeding back from the venturi into the fuel chamber. 78).
L68-69 HD1C gets the pump check.79)
70-71 HD1D different body casting. may be different low speed circuit.80)
HD-2A
HD-2AB
HD-2B
Electra Glide models 81)
w / pre lever needle and seat assembly
HD-2AC
HD-2C
Electra Glide models 82)
with new lever needle and seat assembly
27804-66Diaphragm Cover without the ball check valve
27804-66ADiaphragm Cover the ball check valve

Tillotson Carbs (1968-1971) 83) 84)

Serial NumberMain Jet
27162-66B85)
27162-66C86)0.053“, 0.055”, 0.059“, 0.057”, 0.061“, 0.063”87)
27155-66RA (XLR)(27823-66R)
27155-70R (XR)(27823-66R)
Torque Specs Inlet Needle Seat 40-45 in/lbs (4.5-5 Nm)
Diaphragm Cover Plug 23-28 in/lbs (2.6-3Nm)
Carb Idle Speed 900- 1,100 RPM 88)

—-

Tillotson Carburetor Pics

Tillotson Carburetor 89)Tillotson Carburetor on a 1971 XLCH 90)Tillotson Carburetor 91)
Tillotson Carburetor 92)Tillotson- Inside view of tickler before installation 93) Tillotson- Diaphragm 94)
Tillotson Carburetor 95)Tillotson Air Cleaner Backing Plate 96)Notes on the 66 throttle shaft:97)
The 66 only choke shaft.:98)

Parts and Services for your Tillotson Carb

Tillotson Carburetor repair/ refresh kit99)

Mikuni (XR-750 racing engines only)

1972-1980

Through 1980, XR-750 engines were equipped with a 36mm Round Slide100) Mikuni. Below is a chart of the standard jetting of these carbs. Final jetting may vary. 101)

36mm Carb TypesMainPilotNeedleNeedle JetSlideAir Correction Jet
VM-36-1
VM-36-4
VM36/39
240256F5159-P42.01.0

1989-2003

Engine upgrades prompted HD to recommend the use of Mikuni's 38mm Flat Slide carburetor (not supplied with the engine kit). Recommended jetting chart below.102)

38mm Carb TypesMainPilotNeedle JetSlide
TM38-85 (47mm spigot dia.)
TM38-86 (43mm spigot dia.)
210-26020-256FM46Q0,Q2,Q44.0
  • Most Mikuni carbs have a backwards Idle mix screw, in to richen, out to lean. 103)
  • The longer carb provides a better signal to the fuel metering business inside. This is why the round slide carb works so well combined with the taper on the slide and needle. The round slide carb will have a wider sweet spot than a flat slide 104) and that equates to better low range. 105)

Mikuni (general application)

38mm Carb TypesMainPilotNeedle JetThrottle ValveJet NeedleAir Jet
VM38-9 (43mm spigot)106)33030Q-22.56DP10.5

Bendix/ Zenith I6P12 Carb (1972-Early 1976)

  • Model 16P12 (standard) is a horizontal plain tube type carb with a fuel bowl, single ring shaped float, an accelerator pump, idle mixture adjusting needle and a throttle stop screw for idle speed adjustment.107)
  • The throttle body casting contains an integral venture and a fuel valve seat that is pressed into the body. The underside of the throttle body contains a long boss that the main jet and discharge tube assembly screw into with the end of the tube projecting up into the venture.108)
  • Note for 1973 and earlier: The change letter (A or B) is stamped near the Basic Bendix carburetor part number (13609) for identifying carburetors with modifications. Idle tube 27749-72 (marked A) is standard on carbs marked with a change letter (A). Idle tube 27750-72 (marked B) is standard on carbs marked with change letter (B).109)
    • Fuel Supply Stream: Fuel under pressure enters the float chamber through the fuel inlet and valve (needle and seat. The bowl fuel level is automatically maintained by the float which opens and closes the needle seat valve to supply varying fuel demands to the engine.110)
    • Accelerator System: The accelerator pump controls the amount of additional fuel discharged into the air system upon sudden throttle opening and it consists of a pump assembly, accelerating jet, check valve and the mechanical linkage connected to the throttle shaft.111)
    • Idle System: Fuel for idle is drawn in from the main metering well through the idle tube and is mixed in the channel leading to the idle discharge holes with air entering the idle air bleed. At low idle speed, throttle plate is positioned to expose only the #1 idle discharge hole to engine vacuum. Air is admitted to the idle channel through the #2, #3 and #4 (1972 and later) idle holes. Air mixes with the fuel/ air mixture in the channel and is discharged through the #1 idle hole. As the throttle plate is opened, the #2, #3 and finally the #4 hole begins discharging fuel/ air mixture to supply the increased fuel required for higher engine speeds. The idle needle regulates the fuel/ air mixture flowing thru #1 discharge hole. Turning the needle clockwise (in) leans out the mixture while turning counterclockwise (out) richens the mixture. The idle speed is set by adjusting the throttle stop screw instead of the idle adjusting needle.112)
    • Choke System: Before cranking the engine, the throttle should be opened to expose all three idle holes. The choke plate should be held fully closed during the cranking. After the engine starts, open the choke slightly. A hole in the choke plate helps prevent over-choking when the engine is started. The choke should be moved to wide open when the engine is partially warmed up.113)
    • High Speed metering System: The fuel for the engine operation from off-idle to full throttle is supplied from the fuel bowl through the main metering jet, metering well and discharge tube. As the fuel flows thru the metering well and tube, it mixes with air entering the well vent to provide the correct fuel/ air mixture ratio for all engine speeds and loads. A series of air bleed holes in the discharge tube permits air from the well vent to enter the bowl below the level of the fuel in the float chamber. This reduces the average density of the fuel and enables it to flow freely at low suction. At high engine speeds, (and high suction), the air to fuel proportion thru the main metering system is reduced to provide a richer mixture needed for peak performance. 114)
  • Features: 115)
    • 38mm116)
    • Integral Float Chamber
    • Low speed needle
    • Throttle stop screw
    • Throttle lever
    • Manual Choke lever
    • Barrel Type Accelerator pump
    • Bowl drain plug
    • ID number stamped on top over the butterfly plate
    • Intake Manifold ( 27021-71A )117)
Year Model XLH/ XLCHSerial NumberMain Jet Sizes (mm)Low Speed Idle Jet
1972-Early 197527155-72 118)0.90mmPart #(27749-72) 119)
1972-Early 197527155-72A 120)'72-early '75 (0.95), '72-74 (1.00,1.05, 1.10, 1.15, 1.20, 1.25mm)Late '72-'74 Part #(27750-72)121)
1975-Early 1976
(also used on '71-'75 FX models)122)
27155-72B123)0.95, 1.00,1.05, 1.10, 1.15, 1.20 mm 124)
Bendix Main Jet Identification 125)
Model InfoHD Main Jet Part #Bendix Main Jet Part #Bendix Main Jet SizeDrill Size
1972-1974 XL, XLCH
1971-1975 FL, FLH, FX, FXE
27612-71
27614-71
27618-71
27619-71
27620-71
27621-71
27622-71
27623-71
C66-173
C66-174
C66-155
C66-156
C66-157
C66-143
C66-158
C66-159
18
19
20
21
22
23
24
25
0.90 mm (0.0354“)
0.95 mm (0.0374”)
1.00 mm (0.0394“)
1.05 mm (0.0413”)
1.10 mm (0.0433“)
1.15 mm (0.0453”)
1.20 mm (0.0472“)
1.25 mm (0.0492”)
1975 and later XL, XLCH
Late 1975 FL, FLH, FX, FXE
27651-75
27652-75
27653-75
27654-75
27655-75
27656-75
C66-183-19
C66-183-20
C66-183-21
C66-183
C66-183-23
C66-183-24
19
20
21
22
23
24
0.95 mm (0.0374“)
1.00 mm (0.0394”)
1.05 mm (0.0413“)
1.10 mm (0.0433”)
1.15 mm (0.0453“)
1.20 mm (0.0472”)
Bendix part # is stamped on the hex head side of the jet. The standard 1.10 mm for 1975 and later carbs is only labeled C66-183. All other jets for '75 & later models have the full # with suffix
Carb Idle Speed 700- 900 RPM 126)

Bendix / Zenith Carburetor Pics

Bendix / Zenith carburetor 127)Bendix / Zenith carburetor 128)
Bendix / Zenith carburetor 129)Bendix / Zenith carburetor 130)
Bendix / Zenith carburetor 131)Bendix / Zenith carburetor 132)
Bendix / Zenith carburetor 133)Bendix / Zenith carburetor 134)
Bendix / Zenith carburetor 135)Bendix / Zenith carburetor 136)
Bendix / Zenith carburetor on a 1974 XLH 137)Bendix / Zenith carburetor on a 1974 XLH 138)

Keihin non-CV Carb (Late 1976-1987)

  • The Keihin non-CV carburetor is a horizontal type with a fuel bowl, single ring-shaped float, an accelerating pump, idle mixture adjusting needle and a throttle stop screw for speed adjustment. 139)
  • The throttle body casting contains an integral venture and a fuel valve seat that is pressed into the body. The underside of the throttle body contains a boss. The main jet screws into the boss and holds the bleed tube in place.140)
    • Operation: Fuel from the gas tank passes through the fuel valve, onto float chamber. The fuel entering causes the float to rise until it shuts off the fuel valve, stopping the flow at a level predetermined by float level setting. 141)
    • Idle or Slow System: The slow system functions at idle, low and intermediate speeds when throttle valve is closed or only partially open. At idle, fuel enters the main jet and, after being metered there, enters the slow jet where it is metered again. Fuel from the slow jet enters the slow jet bleed tube where it mixes with air through the slow air passage. Fuel mixture is regulated by adjusting the idle (low speed) mixture screw. When the throttle valve is closed, fuel mixture flows into the venture almost entirely through the idle port. As the throttle valve gradually opens, fuel mix discharge is transferred to the bypass. The slow jet bleed tube is actually a part of the slow jet. 142)
    • The Main System: The main system functions at intermediate and high speeds as the throttle valve opens further. Fuel is metered by the main jet and enters the main jet air passage. The fuel/ air mixture then exits from the main nozzle and into the venturi. 143)
    • The Accelerating Pump System: The accelerating pump system works with sudden throttle openings (rapid acceleration) to quickly inject fuel into the carb to provide extra fuel for the engine demand. Rapid throttle action pushes the pump rod down, flexing the diaphragm, which compresses fuel underneath the diaphragm, forcing it up past the check valve and out the pump nozzle into the venturi. The check valve prevents backflow while the pump nozzle meters the flow. Spring action then returns the diaphragm back to it's original position. As the diaphragm returns, a new supply of fuel flows in and under it so the system will be ready to repeat the cycle with the next rapid throttle action detected. 144)
    • The Choke System: The choke is manually set by pulling out on the choke button. Pulled all the way out is fully closed (for cold engine), partially open (for warm engine) or pushed all the way in, fully open (for warm engine). 145)
  • Additional Tips on usage:
    • Make sure the low speed and main jets are larger than stock to match the more free-flowing aftermarket exhausts and air filters we all seem to run. 146)
    • Do not run a worn out ignition auto advance unit. It makes carb farts that you would swear were lean low speed mixture.147)
  • Integral Float Chamber
  • Manual Choke
  • 3 different models
  • Model Year Changes
  • Tuning
  • The usual method to set idle mixture/speed is:
    • First: Set idle MIXTURE screw to 7/8 turns out. Get the bike hot. Set idle at comfortable speed with the idle SPEED screw. 148)
    • Second: Adjust the idle MIXTURE screw to the point where engine runs the fastest. This is optimum mixture. 149)
    • Third: Adjust idle SPEED screw again to get desired idle speed. 150)
  • The spring on the idle speed screw tends to creep the idle speed back up if you try to adjust the idle just that little bit slower. So I adjust the idle speed screw right down too slow, then nudge it up slightly faster until I get the speed I want, then it stays there. 151)
  • If your bike idles best with the idle mixture screw less than ½ turn open, you need a smaller low speed fixed jet. 152)
  • If your bike idles best with the idle mixture screw more than 1-1/4 turns open, you need a larger low speed fixed jet.
  • This is real important. It also is the way to stop “carb farts” – spitting back or backfiring through the carb.
    • If your Ironhead has aftermarket free-flow exhaust and airfilter on it, it will almost certainly need a larger low speed fixed jet, and most likely a bigger main jet too. But it is the low speed jet that affects the dreaded carb farts. Main jet affects mixture at wide open throttle and if left lean can overheat the engine, or burn holes in pistons. 153)

Late 1976-Early 1978

  • Features:
    • 38mm venture 154)
    • Pump adjusting screw
    • Idle mixture Screw
    • Throttle stop screw
    • Rocker arm
    • Intake manifold ( 27021-71A )155)
    • Accelerator pump rod attached at throttle cam 156)
    • New diaphragm accelerator pump 157)
    • Optional main jets were made available 158)

Late 1978-1980

  • Features/ Upgrades:
    • Changed to 34 mm venture 159)
    • Fast idle cam screw
    • Limiter Cap (over idle mixture )-late 1978-1979
    • Idle mixture screw is set and sealed off (1980) at the factory due to EPA regulations
    • Throttle stop screw, throttle lever
    • Choke plate
    • Choke lever shaft
    • Mounting flange
    • Accelerating pump lever
    • Rocker arm
    • Intermediate lever
    • Fast idle cam
    • Accelerator pump housing redesigned in 1979 160)
    • Optional high altitude modification kit (1979)

1981-1983

  • Accelerator pump
  • Features/ Upgrades:
    • Throttle lever
    • Throttle stop
    • Fast idle cam
    • Fast idle cam adjusting screw

1984-1985

  • Features/ Upgrades:
    • Throttle lever
    • Throttle lever stop
    • Voes vacuum port
    • Fast idle cam
    • Fast idle cam adjusting screw

Carburetors by Bike Year Model

ModelYear
Carb Used
Serial NumberFlange
Number
Main Jet SizeLow Speed Jet SizeIdle Mixture
turns open
Accel Pump
spring position
XLH, XLCHLate 197627153-76161)B50A 162)(140 std) 163)
Optional jets made available 164)
- 130, 135, 145, 150
155, 160, 165, 170, 175165)
1007/8 166)Upper 167)
XLH, XLCH, XLT1977-1978 27153-77 168)B50B 169)
B50C
(160 std) 170) (165 std) 171)
Optional jets made available 172)
- 130, 135, 145, 150
155, 160, 165, 170, 175173)
751-1/4 174)Center 175)
XL, XLCH, XLS 197927469-78A 176)B83A165 (160 - above 4000') 177)0.65 mm178)
XL, XLS198027469-80AB83D1600.65 mm 179)
XL, XLS1981-Early 198227469-81AB83F1600.68 mm 180)
XL, XLSLate 198227469-82B83G1500.68 mm 181)
XL, XLS, XLX1983-198527469-83CB83K1600.52 mm 182)
XLCR 1000 183)1977-197827148-77B60A
B60B
185901-1/8 184)Upper 185)
XLCR 1000
quiet engine 186)
1977-27146-77B75A175901-1/2 187)Upper 188)
  • Carburetors with the latest letter stamped on the flange have improved sealing on the welch plugs, throttle shaft ends and idle mixture screw. 189)
  • Carb Idle Speed: 900 RPM 190)
  • Torque Specs:191) Late 1976-1985, Carburetor Mounting Nuts - 19 ft/lbs (26 Nm)

Keihin non-CV pics

1977 Keihin 38mm non-CV pic 1192)1977 Keihin 38mm non-CV pic 2193)

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2) , 9) , 33) , 34) , 35) , 36) , 37) , 38) , 39) , 40) , 41) , 53)
1959-1969 HD Sportster FSM
3) , 6)
1952-1959 HD Spare Parts Catalog pg 15
4) , 5)
1952-1959 HD Spare Parts Catalog pg 14
7) , 8)
1952-1959 HD Spare Parts Catalog pgs 15,16
11)
1952-1959 HD Spare Parts Catalog pg 16
14) , 17) , 20) , 23) , 30)
HD 1959-1964 Sportster FSM
54) , 55) , 56) , 57)
Photos courtesy of xlh59 of the XLFORUM http://xlforum.net/forums/showthread.php?t=1914726&page=2
61) , 64) , 65) , 67) , 68) , 69) , 70) , 71) , 107) , 108) , 109) , 110) , 111) , 112) , 113) , 114) , 139) , 140) , 141) , 142) , 143) , 144) , 145)
1970-1978 HD XL/XLH/XLCH/XLT 1000 FSM
62) , 63)
1970-1978 HD Sportster FSM
66)
HD Service Bulletin #571 dated May 21, 1968
72)
1959-1985 Clymer Sportster Service and Repair Manual pg 76
73)
HD Sportster Parts Catalog (99451-78B)
75) , 76) , 81) , 82)
HD Service Bulletin #547 dated October 24th, 1966 pg OC-237
78) , 83) , 85)
Shop Dope Vol 4 Service Bulletin No 571 May 21, 1968
84)
1970-2010 Haynes Sportster Service and Repair Manual pg 3.1
86) , 87)
HD Sportster Parts Catalog pg B11-1 (99451-78B)
88) , 126) , 190)
Clymer Sportster Repair Manual 1959-1985
89) , 90) , 91) , 92) , 93) , 94) , 95) , 96) , 99) , 127) , 128) , 129) , 130) , 131) , 132) , 133) , 134) , 135) , 136) , 137) , 138)
Pic courtesy of The Doctor71 of the XLFORUM
101) , 102)
1972-2003 HD XR-750 Service Manua pg 39
115)
1959-1985 Clymer Sportster Service and Repair Manual pg 78
116)
HD XLH,XLCH-1000 Parts Catalog (99451-78B)
117) , 123) , 155)
HD Sportster Parts Catalog (99451-78B)
119) , 124)
HD Sportster Parts Catalog pg 27 (99451-78B)
121)
HD Sportster Parts Catalog pg 28 (99451-78B)
122)
1971-1984 HD FX Parts Catalog pg 35
125)
Shop Dope Service Bulletin #697 dated March 29, 1976
156) , 157)
HD XLH XLCH-1000 Parts Catalog (99451-78B)
158) , 164) , 172)
HD Parts and Accessories Bulletin dated February 8, 1977
160)
HD Sportster Parts Catalog pg 17
161) , 165) , 168) , 173)
HD Sportster Parts Catalog XLH/XLCH 99451-78B
162) , 169)
HD Service Bulletin #M-713 dated June 10, 1977
163) , 166) , 167) , 171) , 174) , 175) , 183) , 184) , 185) , 186) , 187) , 188) , 189)
HD Service Bulletin #M713 dated June 10, 1977
170)
1954-1977 HD Sportster Parts Supplement pg 2
176) , 178)
1979 Harley Davidson Sportster Parts Catalog
177)
HD Service Buletin #M-730 dated June 15, 1978 - Instruction Sheet pg 2
179)
1979-1985 HD XL Parts Catalog pg 23
180) , 181)
1979-1985 HD XL Parts Catalog pg 25
182)
1979-1985 HD XL Parts Catalog pg 27
191)
1970-2010 Haynes Sportster Service and Repair Manual pgs 3.1-3.2
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