What is a Harley CV carb?

A CV carburetor (Constant Velocity) incorporates a vacuum operated slide that varies the venturi size within the carburetor, thus maintaining a constant velocity. The slide also holds a needle that when lifted by the opening slide varies the amount of atomized fuel delivered.

How do you tune a Harley Davidson CV carburetor?

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.

How does a Harley CV carb work?

Unlike aftermarket carburetors using throttle controlled slides or butterfly valves, the Harley CV made by Keihin uses a vacuum actuated slide. The unique design constantly changes the size of the venturi (throat) based on manifold vacuum while simultaneously metering the air/fuel delivery.

What size pilot jet should I use?

The pilot jet is sized correctly if the fuel screw setting falls between 2.5-3 turns out. The pilot jet is sized correctly if the air screw setting falls between 1-2 turns out, with 1.5 being the sweet spot.

What happens if main jet is too big?

For example, using too large of a main jet will cause more fuel to enter the combustion chamber than it can efficiently burn. This will result in a “sputter” at full throttle. It could best be described as a rapid misfire.

Does main jet affect idle?

The main jet does not effect the jetting for starting and idling. It plays no part on low RPM or mid RPM jetting either. The main jet is very important to your machines overall tuning, but should never be over emphasized at the expense of needle tuning or other facets of your carburetion tuning.

How do I know if my carburetor is clogged?

Symptoms of a Bad or Failing CarburetorReduced engine performance. One of the first symptoms commonly associated with a bad or failing carburetor is a reduced engine performance. Black smoke from exhaust. Another symptom commonly associated with a problematic carburetor is black smoke coming from the exhaust. Backfiring or overheating. Hard starting.

Which way do you turn the idle screw?

Turn the idle adjustment screw clockwise with a Phillips screwdriver to increase the engine’s idle speed. Turn the screw counterclockwise to lower the idle speed. Adjust the engine idle speed so that the motor is running smoothly without chugging or racing.

Which way do you turn a carb mixture screw?

Turn the screw back clockwise until it is approximately in the middle location between where the engine’s idle sounds irregular and rough. This will set the engine at a regular idle speed.

Is it better to run lean or rich?

Running lean can give you more power but to lean will blow your engine. Running too rich can also hurt your motor. Think of it when you are mixing gas for your weed wacker. It is always safe to add a little more oil than not enough to the mixture.

What is a bad air fuel ratio?

If the ratio is too rich or too lean, the engine will not burn optimally burn the air-fuel mixture which can cause performance issues or use up too much fuel. The ideal air-fuel ratio that burns all fuel without excess air is 14.7:1. But at some conditions, not all fuel can be mixed and vaporized with air.

What is a rich air/fuel ratio?

When the air-fuel ratio is higher than the stoichiometric ratio, the air-fuel mixture is called lean. When the air-fuel ratio is lower than the stoichiometric ratio, the air-fuel mixture is called rich. For example, for a gasoline engine, an AFR of 16.5:1 is lean and 13.7:1 is rich.

How do you fix air fuel ratio?

The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required.

What should air fuel ratio be at WOT?

We mentioned the stoichiometric air-fuel ratio (14.7:1) that is the ideal ratio for lowest emissions, but this isn’t the best ratio for power. It used to be that 12.5:1 was considered the best power ratio, but with improved combustion chambers and hotter ignition systems, the ideal now is around 12.8:1 to 13.2:1.

What causes bad air fuel ratio?

Problems with air fuel ratio sensors are common. Often a sensor gets contaminated or simply fails. In some cars, the heating element inside the sensor fails causing the malfunction. For example, in many Toyota and Honda cars the code P0135 may be caused by a failed heating element inside the sensor.