Harley CV Carburetor Mixture Tuning

Mixture tuning on your Harley Davidson CV carburetor is a simple procedure that can easily be performed with basic tools. The mixture screw or EZ-Just is the key to propertuning. These tuning steps apply to all Harley CVcarbsfrom 1989 to present that use the CV 40mm style Harley Davidson carburetor but also apply to the CVK40 found on other models. Always start with a fresh set of spark plugs when tuning.

The carburetor will need to be removed from the manifold so referto yourfactory shop manual for this procedure.
With the carburetor removed, place upside down on a sturdy work surface. The picture below shows the float bowl removed however there is no need to remove the bowl and this will also prevent debris from entering the carburetor or from accidentily disturbing the float setting.

Picture of EZ-Just when fully seated prior to adjustment:

Reinstall the carburetor back on your bike by reversing the steps taken during removal. Be sure to replace the fuel hose clamp, cables, and vacuum lines in the exact same location. Make certain the carb firmly seats back onto the manifold boot as a proper seal is critical. Test the throttle for binding and smooth operation.

The air cleaner assembly must be installed priorto starting the engine, not only to hold the carburetor in place but to prevent having the carburetor backfire in toward you while tuning. Start the engine as normal and bring up to operating temperature priorto fine tuning. Let the bike idle for no more than 5 minutes.

With the engine warmed up and at idle you may now fine tune the idle mixture screwfor optimal performance. Acquaint yourself with the adjustment screw location at the bottom rear of the carburetor priorto running the engine. You will need a small screw driver for adjusting the screw unless an EZ-Just has been installed. With the engine idling slow (no more than 900 rpm), turn the screw inward (clockwise) SLOWLY until the engine starts to stumble. You are working with the screw upside down so check to make sure you are turning the screw clockwise or inward. Note that not all engines will stumble or have an RPM change that is noticable when twisting in the mixture screw. This can be due to the idle jet being too large, installed cams, or ignition systems such as those on Twin Cam 88‘s. If unable to find the low adjustment point where the idle slows, simply set the screw at 1 -3/4 turns out and proceed to the next step.

If the engine will not idle on its own during this procedure, adjust the idle set screw on the throttle side of the carburetor until it idles correctly. Now turn the mixture screw outwards (counter-clockwise) until the engine begins to run smoothly, then add 1/8 of a turn. Maintain proper idle speed and repeat the adjustment each time you adjust the idle speed. Blip the throttle a couple of times and observe the results. If the engine responds quickly with a smooth blast and no backfiring through the carburetor, you have your idle mixture right. If a hesitation occurs then adjust the idle mixture screw out another 1 /8 turn. Normally, the mixture screw should only require 2 to 3 turns out from gently seated. Anything above 4 turns indicates the pilot jet is too small.

Typical wiring diagram for 1980 through 1983 FX models, except FXR (FXB/FXS/FXSB/FXEF shown)-later models similar 

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