How to Adjust the Air Mixture on a 2005 Harley Davidson CV Carburetor


To better meet federal air pollution control standards, 2005 Harley CV (Constant Velocity) carburetors come equipped with a plug that must be removed before you can access the air-mixture adjustment screw. Harley owners are expected to keep the air mixture as it was set at the factory. That setting is slightly too lean, which means the mixture of air and gasoline has slightly too much air. The lean setting improves gas mileage and reduces gas exhaust emissions, but it robs your engine of power. Before you can adjust the air mixture you must remove and modify the carburetor.

Things You'll Need

  • Complete set of mechanics tools
  • Workbench
  • Electric drill
  • 1/16-inch bit
  • Machinist's awl (recommended)
  • Black touch-up paint
  • Masking tape
  • Hose clamp
  • Clean shop rags
  • Remove the air cleaner cover. Disconnect the breather tubes. Remove the air cleaner and the air cleaner backing plate.

  • Shut the petcock. Start the engine and allow it to run until the carburetor runs out of gas. Remove the choke cable from the mounting bracket on the left side of the motorcycle. You will remove the choke cable with the carburetor. Disconnect the fuel line from the carburetor. The line is probably attached with a hose clamp and you will need a replacement clamp when you reattach the line. Label both throttle cables with masking tape and disconnect them from the throttle cam.

  • Rock and coax the carburetor out of the rubber boot by which it is attached to the intake manifold. Label and remove all vacuum hoses with tape.

  • Set the carburetor upside-down on a bed of clean rags on a workbench. Find the aluminum plug in the bottom center of the carburetor. The plug conceals the air-mixture adjustment screw. Use an electric drill and 1/16-inch bit to drill about 1/8 inch into this plug. Use a small machinist's screw or a machinist's awl to gently pry the aluminum plug out of the carburetor.

  • Mark a small flat-head screwdriver with black touch-up paint so you can count the revolutions the screwdriver turns. Use the screwdriver to turn the air-mixture adjustment screw clockwise until it seats. Count the revolutions and do not over-tighten. Turn the screw counterclockwise 1/4 turn beyond your original starting point.

  • Reinstall the carburetor, throttle cables, rubber boots, fuel line, choke, breather tubes and air cleaner assembly.

  • Open the petcock, shift into neutral and start the motorcycle. Use the small screwdriver to adjust both the idle-mixture screw on the top of the carburetor near the throttle cam and the air-mixture adjustment screw on the bottom of the carburetor. You are done when your motorcycle idles without stumbling and accelerates cleanly.

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  • Photo Credit moteur de harley image by fxprod from
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