From 1986-1987, the stock Sportster carburetor was a Keihin 34mm, fixed-venturi “butterfly” model, as used on the Ironhead models from 1979L onward (BT models still used the 38mm version). Contrary to popular folklore, all Keihin non-CV carbs did come with accelerator pumps.

In 1988, the stock Sportster carburetor was upgraded to a Keihin 40mm, slide-type, constant-velocity model. It was quickly discovered that the lack of an accelerator pump was a shortcoming. To help that situation, a special needle, identified as 27094-88 or N65C, was used to help off-idle performance in the 1988 models.

In 1989 and thru 2006, the Keihin CV40 carburetors were produced with an accelerator pump to smooth out initial throttle response.

• 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. ¹⁾
• The throttle body casting contains an integral venturi 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.²⁾
  • 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. ³⁾
  • 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 venturi 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. ⁴⁾
  • 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. ⁵⁾
  • 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. ⁶⁾
  • 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). ⁷⁾
• Integral Float Chamber
• Manual Choke
• 3 different models
• 1976L-1978 have 38mm Venturi
• 1979-1987 have 34mm Venturi
• Model Year Changes

1986-1987 Features ⁸⁾

• 34mm Venturi
• Horizontal, gravity fed with a float operated inlet valve
• Throttle stop screw
• Fast idle cam
• Choke system with fast idle adjustment
• Accelerator pump
• Designed to control exhaust emissions
• Fixed jets
• Factory preset idle mixture

• Note: Main and slow jet sizes are the same for the 86-87 883 and the 86 1100 carbs. But, due to internal differences, the carbs are not interchangeable.¹⁷⁾

(Factory Installed Carbs)

1977 Keihin 38mm non-CV pic 120)	1977 Keihin 38mm non-CV pic 221)

—-

• Used in the Screaming Eagle Package line from HD as an Evolution XLH HI-FLO Carburetor & Air Cleaner. The carb was a (27001-88)
• Adjustable Accelerator Pump stroke
• Incorporated a special intake manifold to carb spacer that had to be drilled and tapped (1/4 x 28) in the side for included Voes connection adapter
• Required a 1987 replacement style intake manifold for 1988 and up models
• Required possible grinding of the right rear corner of the front cylinder head, due to interference with the carburetor throttle pulley and cable guides, for proper clearance ²²⁾

²³⁾

*in carburetor

• Constant velocity-gravity fed/ has a float operated inlet valve and a variable venture.

• The carburetor atomizes gas in proper proportions to the air pulled in through the air intake. At idle, a small amount of gas is siphoned through the pilot jet by the incoming air. The more the throttle is opened, the air begins siphoning through the main and needle jets. The tapered needle increases the flow of the needle jet as it is lifted since it's taper gets smaller as it sets inside the needle jet thus allowing for more flow when lifted up and out. Vacuum from carbs intake,the engine side of the throttle plate, is used to lift the slide barrel/ needle jet. At full throttle, the carburetor venturi is fully opened and the needle is lifted far enough to allow the main jet to flow at full jet capacity. The choke circuit is actually the starting enrichment valve system. The choke knob opens an enrichment valve. With the choke knob in the open position, the slow jet sends a stream of gas into the carburetor's venture thus enriching the gas/air mixture when the engine is cold. The accelerator pump circuit injects a fine spray of gas into the carburetor intake during sudden acceleration to reduce engine hesitation.

Serial Number:

• Labeled on the adjacent side to the accelerator pump linkage

Example 27231-98 translates to

• All CV models come equipped with accelerator pump unless noted.
• All data below is compiled from HD Parts Catalogs unless otherwise noted.
• Sportster models are divided into 3 categories: Domestic, California & HDI models
• See also:
  • California models
  • HDI models
• See Discrepancies in the FSM(s) / Parts Catalog(s) for further information on highlighted * areas in the carburetor charts below
• See also Pics of Keihin CV Carbs That Were Factory Installed on Sportsters

Example Parts Shown Here »>


All CV40 carbs use the following parts & P/N:

27100-88 - Needle Jet
27101-88 - Emulsion Tube (Needle Jet Holder)
27585-88 - Vacuum Slide (Vacuum Piston)

• All CV models come equipped with accelerator pump unless noted.
• All data below is compiled from HD Parts Catalogs unless otherwise noted.
• Sportster models are divided into 3 categories: Domestic, California & HDI models
• See also:
  • Domestic models
  • HDI models
• See Discrepancies in the FSM(s) / Parts Catalog(s) for further information on highlighted * areas in the carburetor charts below
• See also Pics of Keihin CV Carbs That Were Factory Installed on Sportsters

• All CV models come equipped with accelerator pump unless noted.
• All data below is compiled from HD Parts Catalogs unless otherwise noted.
• Sportster models are divided into 3 categories: Domestic, California & HDI models
• See also:
  • Domestic models
  • California models
• See Discrepancies in the FSM(s) / Parts Catalog(s) for further information on highlighted * areas in the carburetor charts below
• See also Pics of Keihin CV Carbs That Were Factory Installed on Sportsters

(Factory Installed) — Click on a picture to enlarge:

Keihin CV40 #27731-04

Used on 2004-2006 (Domestic models) 1200C, 1200R54)

Keihin CV40 #27498-96A

Used on 1998, 2002-2003 (California models) 1200, 1200C 55)

Upon perusing 1986-2006 Parts Catalogs for carburetor information, it's clear that the MoCo was trying to save space in these books at the expense of legibility. Below is a chart showing the initial intentions on the top and the MoCo's mis-interpretations on the bottom. They give no notations (from year to year book) on any changes to the nomenclature. I.E. one way to display a year/ model number is displayed differently in other year books. This chart is not complete nor factual in numbering but as an example only. For instance:

Found and documented discrepancies are in the chart below. I'm sure I didn't list them all ⁵⁶⁾