Common 8 Harley Davidson CV Carburetor Troubleshooting 2024

The process of Harley Davidson CV carburetor troubleshooting is very essential when trying to detect the problem of your Harley Davidson carburetor.

Your motorcycle carburetor might develop some fault as a result of constant use.

Do not worry about this as it can be resolved by troubleshooting the problems and doing the necessary things to make it work perfectly again.

Carburetor troubleshooting means detecting the problem that has been developed by your motorcycle.

When the carburetor develops a fault, it won’t make your motorcycle function very well, so you have to troubleshoot the problems and find a necessary solution to it yourself or seek the assistance of an expert.

In this guide, we will be talking about Harley Davidson troubleshooting problems and the necessary solutions. Without further ado, let’s get started.

What is a Harley CV Carburetor?

As we have all known Harley Davidson is an established brand, they make use of CV (Constant Velocity) carburetor as opposed to the throttle controlled valves of the other engine carburetors.

The Harley Davidson CV carburetor is designed by Keihin, it works in a different way to the other carburetors, the throttle changes based on the vacuum generated by the engine and also helps to reduce the fuel consumed by the engine.

Overall, the constant velocity carburetor is the best and that’s why it has been used in the Harley Davidson motorcycles.

How Does Harley CV Carburetor work?

A carburetor is an important part of the motorcycle engine, it helps to blend the air as fuel that is needed for combustion without any help from the sensors or even the electricity powering the bike.

A carburetor is designed in the form of a cylindrical tube in which air comes in from the upper part and the combustion chamber is placed at the lower part.

The carburetor fluid is higher which in turn decreases the pressure inside the carburetor.

There is a hole inside the carburetor which leads to the fuel reservoir, so because the pressure is reduced, the fuel consumption is also minimal.

When the motorcycle is ignited, air enters into the carburetor through the side and goes straight into the combustion chamber where combustion takes place.

There is also a butterfly valve that is connected to the throttle and when the throttle is opened, the butterfly valve is also opened. As this happens it keeps the engine working constantly.

How to Adjust the Idle on a Harley CV carburetor

Adjusting the carburetor idle means reducing the rate at which air and fuel mix together in the carburetor.

At idle, which means when the engine is not working or moving, the carburetor throttle will be about to close and the air flows along the air horn is impeded to generate enough fluid into the venturi.

So to adjust your carburetor idle, there is a screw on the right side of the throttle, locate it, and whenever you notice your engine will not idle properly, adjust the screw until you get the desired idle that you want.

Harley Davidson CV Carburetor Troubleshooting

Whether it is accelerator pump adjustment issues or needle adjustment problems, a dysfunctional carburetor could negatively impact how you enjoy your bike.

Troubleshooting is the answer to many of the carburetor problems that could ruin your bike.

This article will dig deep into some of the very common carburetor problems and some proposed solutions for them.

1. Popping and Stalling

This is a common problem of a constant velocity carburetor. There are a lot of factors that can cause a carburetor to pop and stall.

The most common reason for a carburetor to pop is when there is a blockage of the fuel flow.

To avoid this you have to clean to make sure fuel flows constantly into the engine.

Another reason why your carburetor might pop and stall is if your motorcycle has a faulty ignition system.

When you ignite your engine, and it sparks the plug, the sparking has to occur at a good timing, or else it will affect the carburetor and make it stall.

Popping and stalling can damage the whole engine if care is not taken, as it will not allow fuel delivery into the engine to go smoothly.

When this happens your motorcycle might work for a while and then stop working because fuel delivery is not constant.

2. Tuning Issues

Your Harley Davidson CV carburetor could indicate that it’s time you get it tuned.

When you start experiencing a radical reduction in fuel economy, sluggish acceleration, emission of black smoke, or hesitation when accelerated, then your suspicion is complete; your bike has tuning issues.

Smearing a tiny silicone grease inside the manifold boot while ensuring that sure the carburetor firmly presses onto the boot address these issues.

3. Adjust Idle Mixture

Idle mixture enables a carburetor to function very well and if it is not done properly, it will damage the engine finally.

The circuit of the idle is an important part of the engine and this will go a long way in improving the response of the carburetor throttle.

The idle mixture should be done properly for the full functioning of the engine even when it is not moving.

4. Exhaust leaks

The liners between the exhaust openings and the head pipes fit that will drip if the pipes are reinstalled, removed, or under/over-torqued.

Cool air channeled to the exhaust at these gaskets leads to popping or hesitation normally misdiagnosed as a carb issue

5. Fuel Probs

Blocked idle mixture loop. A bunch of small tubes links the mixture screw, pilot jet, and air intake jet situated on the frontal part of the CV carb.

Debris or lacquered old gasoline will jam these channels, resulting in motor slowness or lean popping.

The fuel has to move constantly into the engine to ensure full functioning. So you need to clear the pathway of the fuel delivery into the engine to avoid this problem.

6. Accelerator Pump Adjustment

Ensure that when you step on the accelerator, gasoline pours from the accelerator pump outlet.

The throttle pump diaphragm will crack or wear with time, especially if it is kept in a fuel-filled CV carb for a prolonged period.

7. Carb Coughing

Carburetor coughing can be caused by a lot of factors. But the most common cause is that the carburetor is weak and needs to be replaced.

Your carburetor might be coughing while idle because it is clogged and there is no free airflow into the engine.

Your carburetor can also cough if there is no enough or too much fuel flow into the engine.

The carburetor should be adjusted properly too for full functioning.

8. Needle Adjustment

Constant velocity carburetors are often associated with needle adjustment problems.

The needle inside the carburetor moves up and down constantly to ensure the full functioning of the carburetor and to ensure a constant supply of fuel into the engine.

As you ignite the motorcycle engine, the needle inside the carburetor moves up and down and the opening gets bigger to allow more fuel into the carburetor.

The carburetor needle needs to be cleaned constantly to ensure it does not clog.

Solution To The Problems

Adjust Idle Mixture

  • Find the idle screw on the bottommost opening of the car, in a pathway close to the floating vessel.
  • Bore out the metallic plug enclosing the idle screw.
  • Use a tiny pick to pry out the plug.
  • Turn the screw in a clockwise fashion.
  • Turn the screw two turns out in an anticlockwise fashion to a speed of one thousand revolutions per minute.

Carb Coughing

  1. Drive your bike.
  2. Administer the Lucas gas procedure, use half the small bottle for every tankful.
  3. Remove the carburetor, put on your glasses, and tidy it up as you’ve always wanted to.
  4. Go one up on the major jet.
  5. Return the gas/air mixture screw to the stock-plus position.
  6. Adjust the idle screw over the following few trips until it’s exactly right.
  7. Keep driving your bike!

Fuel Problem

  • Pull out the pilot jet from the Harley carburetor.
  • Take out the mixture, spring, washer, and o-ring screw.
  • In the pilot jet route and mixture screw passage, spray a little quantity of mild carburetor or fuel injection cleaner.
  • Let no cleansing liquid come into touch with the mixture o-ring screw or the sliding diaphragm.
  • Utilize pressurized air to flush the passages.
  • Begin by blocking the pilot route hole using your finger and spraying the mixture screw opening with pressurized air via the nozzle. Air will emerge from the air intake jet.

Needle Adjustment

  • Check to see if the needle is properly adjusted. Upside down installation of the jet will negatively impair needle metering and fuel spray.
  • Position the needle jet correctly if it is not correctly positioned
  • You can opt for a replacement if the needle jet is worn or missing.

How to Clean CV Carb

  • Clean excess junk, oil, dirt and from the exterior of the carburetor using brake clean
  • Remove the springs, vacuum diaphragms, and top covers.
  • Remove the o-ring and small washer from the screw hole.
  • Remove the boots and intake plate
  • Immediately wash your skin if it touches it.
  • Remove and tidy up the big o-rings.
  • Clean the body of the carburetor.
  • Employ face shield /glasses/ safety goggles, pump out every pathway with pressurized air.
  • If you find any gunk at the float bowl’s bottom, scrape it using a small screwdriver.
  • Re-affix the boots and intake plate. Do not forget the large o-rings!
  • Install float needle seats, pilot jets, and main jets.
  • Install spring, mixture screw, o-ring, and washer. Turn it so that it lightly seats in the bottommost part of the threaded opening.
  • Install floats and float needles. Set the float height aright.
  • Check to see if the float bowl is flat or cracked. Replace if either is true.
  • Install the float bowls.
  • Install springs and diaphragm.
  • Install diaphragm upper covers.
  • Install the carburetor on your bike and synchronize.

Frequently asked Questions Harley Davidson Carburetor Problems

How Would You Tweak The Float On A CV Carburetor?

A Harley CV carb’s float level is changed by carefully twisting the metallic tab that emerges from the float and rests on the float needle plunger.

What Could Make My Harley Davidson Backfire?

A small explosion in the exhaust or intake causes Harley Davidson to backfire. This backfire is intended to occur in Harley’s combustion chamber.

It’s usually caused by a problem with the exhaust system or engine’s activities.

What Is The Best Way To Reset A Carburetor?

Set the carb to the “original” setting if it has been replaced or is still new. Tighten the idle screws to 1.5-2 turns outside and the idle screw to 1-1.5 turns inside to achieve this.

Warm up the engine. The correct fuel and air mixtures are closely related to the engine’s operating temperature.

How Would You Adjust A Carb On A Bike?

Start the motorcycle and let it warm up to the running temperature. Set the idle speed screw to raise speed or reduce speed by turning it clockwise.

The idle speed range ought to be between 950 and 1050 revolutions per minute. You may alter the idle mixture by gently moving the idle screw in a clockwise fashion until the engine runs inadequately.

Why Would A Carb Overflow?

When the valve’s opening wears down or dirt stops the valve from closing, fuel pours continually into the pan, overflowing the engine compartment.

Fuel may saturate the overflow or air filter out of the carb and on the floor while seated under extreme circumstances.

Is It Dangerous To Allow A Bike To Idle?

Idling a motorbike isn’t always a bad thing, as long as it’s done in moderation. In comparison to air-cooled bikes, liquid-cooled motorbikes can withstand idling well, and the temperature must be put into consideration while allowing your air-cooled engine to idle.


The above Harley Davidson CV carburetor troubleshooting instructions are simply intended to serve as a reference to help with some frequent problems that you may periodically encounter.

While it is true that the list is not an exhaustive treatise, it furnishes you with most of the knowledge you need to troubleshoot your Harley Davidson bike.