Carburetor Jetting on a Harley-Davidson

Carburetor Jetting on a Harley-Davidson

Aug 11, '20

Routine motorcycle maintenance, like carburetor jetting, is the key to efficient, responsive riding. Not only will it keep your Harley-Davidson bike running right, but it will help you to save money on expensive repairs, reduce the risks of accidents, damage, wear and tear on essential parts and systems, and make every ride smooth and comfortable.

One routine service you will want to be familiar with when maintaining your bike is carburetor jetting. In layman’s terms, this process is designed to help you balance the fuel to air ratio, so your bike’s engine can run at optimal capacity. You can perform this relatively straight-forward task at home with the tools you already own and the parts available here at Demon’s Cycle. This Harley Carburetor Jetting guide has the info you need to know when it comes to keeping your motorcycle safe, efficient, and ready to hit the road.

Do I Need to Jet My Carburetor?

You may be wondering if this process is even necessary for your motorcycle. There are a few simple ways to determine whether or not you need to jet your carburetor now or in the future.

First though, let’s figure out if you have a carburetor on your Harley-Davidson motorcycle. In the mid-to-late 1990s, Harley Davidson started to embrace some of the changes that were taking place across the motorcycle and automotive industry by providing motorcycles available with electronic fuel injection, rather than carburetors. Starting in 1996 the first models appeared with fuel injection. They were the FL-series Touring bikes and fuel injection was an option.  Eventually, outside pressures, a rising wave of young Harley-Davidson enthusiasts, and the benefits of new technology in ride comfort, performance, and motorcycle responsiveness, meant that Harley-Davidson carburetors were to become a thing of the past. In 2008 all Harley-Davidson models came standard with fuel injection and the carburetor was finally dead, at least on production bikes. The accessibility and ease of working on a carburetor holds a certain amount of appeal, which is why it is still the preferred choice on custom built motorcycles.

If you’re lucky enough to own a Harley-Davidson bike with a carb or you’ve retrofitted your new model, this guide is for you.

Your spark plugs are an excellent indication as to the overall health of your motorcycle, so begin by taking them out and inspecting them. If your plugs are clean, that means your calibration is appropriate and you don’t need to worry about jetting your carburetor. However, if they’re another color, that is an indication that something in the system needs to be adjusted. If you notice that your spark plugs are black and covered in soot, it’s a sign that you have too much fuel and not enough air making its way to the engine. Inversely, if your plugs are white, that means you have too much air and not enough fuel. This is referred to as running rich or running lean.

You can also determine if you need to make calibration adjustments by jetting your carburetor simply by paying close attention to the ride experience. A motorcycle that is slow to respond or appears to be backfiring often is likely getting too much fuel, while a motorcycle that has quick acceleration off the line but seems slow or lacking in overall power once in motion may be getting too much air. You may even be able to hear the issue when riding or idling in the form of popping or other unusual sounds. Remember, there are two main jets that control your bike’s fuel intake at different throttle levels, so listen at high and low throttle levels for indications of a problem.

And don’t worry if you find one. The adjustments are easy to make at home and you’ll be feeling the improved ride right away.

What to Consider Before You Begin Harley Carburetor Jetting

  • Where do you live? Your environment plays an essential role in how you jet the carburetor on your Harley, so consider the average climate, humidity, and altitude of where you drive before you begin. You’ll also want to think about adjusting your jets if your environment is about to change considerably, specifically in relation to altitude or humidity levels. 
  • What kind of upgrades or adjustments have you made to your bike? These can be an excellent way to add power or improve facets of performance or ride, but they can also be the reason your motorcycle is running rich or lean. Keep any custom additions or repairs in mind when you begin your jetting process and consider how they might affect your motorcycle’s fuel to air ratio. 
  • How old is your bike? The age of your Harley-Davidson motorcycle should be accounted for, as motorcycles produced before 1989 are equipped with older style carburetors called butterfly carbs. Motorcycles produced after 1989 had Keihin CV or constant velocity carburetors, which are safer, more reliable, and better at maintaining velocity. You may want to consider upgrading your butterfly to a CV carb at this stage if you have an older motorcycle.

Tools and Parts

If you’ve gotten this far and you’re still ready to begin the Harley carburetor jetting process, there are a few things you’ll want to have on hand: 

  • Screwdriver
  • New jets
  • Camera or phone
  • Your service manual 

Step One: Drain Your Carburetor

This is a simple step, but it does require some patience, since you want to ensure your carb is entirely drained before you begin. You’ll want to begin by shutting off your petcock valve, which will prevent fuel from moving from your tank into your carb. Then you can either drain the carb by unscrewing the drain plug and allowing the excess fuel to flow into a pan or you can simply run the engine while the bike is in neutral. When you begin to hear a sputtering or stalling sound, the carb is nearly dry, but always be careful when removing it, as there will likely be residual fluid.

Step Two: Remove the Carburetor

This is why you’ll want to have your owner’s manual on hand, since each bike will have a slightly unique set-up. Removing the carburetor is relatively simple, but it’s a good idea to know exactly what you need to do before you begin the process. You may find that you have to remove the seat or the gas tank or other systems to ensure easy access. We recommend taking pictures with your phone or camera at each stage so you can easily return things to the way they were once the job is complete.

Step Three: Remove Hoses and Ancillary Connections

Now that your carburetor has been removed, you’ll be able to see if there are any other hoses or parts in the way of you performing your carburetor jetting process. To the best of your ability, you want to remove these parts and place them safely to the side. Remember, a few photos at each stage will make it that much easier to put everything back together correctly when it’s time.

Step Four: Remove the Float Bowl and Gasket

The motorcycle float bowl is designed to help maintain fuel levels in your motorcycle and prevent flooding. A few screws hold the float bowl and its requisite gasket in place, and you’ll want to carefully remove both and place them off to the side. You should now have access to the main jet and the pilot jet. Each jet monitors and balances fuel amounts at different throttle levels, with the pilot jet (or jets) at the lower end and the main jet at the upper end.

Step Five: Install New Jets

This is actually step one and step five, since you’ll need to have a sense of which jets are appropriate for your bike before you can begin the process. You can refer to Carburetor Size Charts to help with this, along with your service manual. Assuming your jets are stock size and have not been customized, you’ll want to consider a jet kit that goes up a single size at a time, to avoid flooding. Reference your service manual for information on which jets you currently have in your bike and which to size up to next. The Demon’s Cycle team is also here to help you pick out the right jets and other Harley Davidson parts, and ensure your motorcycle is running at optimum capacity. 

There is helpful information on the side of the jets themselves that will make it easy to determine how to add more or less fuel, as well. The numbers on the jets coincide with the size of the holes. The larger the hole, the more fuel in your carburetor and vice versa. 

Be careful when it comes to adjusting your jets, though. If you make too many changes to the individual jets at the same time, it can be difficult to know what the original problem was and whether you fixed it or adjusted incorrectly in the other direction. Consider adjusting one jet at a time and seeing how your motorcycle responds.  

It’s also worth noting that you may not need to replace your jets at all. If your jets have become clogged from debris in the fuel, simply cleaning the carb jets will go a long way to balancing your air to fuel ratio.

Step Six: Adjust the Jet Needle

Now that your jets are installed, you’ll want to adjust your jet needle to ensure that it is in line with your new jet size. The jet needle is designed to control fuel flow between ¼ and ¾ throttle—or in between when the pilot jet and the main jet control fuel flow. To access it, remove the carburetors' top cap, along with ancillary parts like springs. The needle will have a small clip close to the top, which will maintain fuel flow. For less flow, move the clip up, which will make the hole smaller. For more flow, move the clip down. It’s essential that you make note of where the clip was when you first found it.

Step Seven: Put it All Back

Congrats–you’ve completed the job. Return the jet needle to its position and begin the process of putting the carburetor parts and other bike parts back into place. This will be much easier if you followed our tip about taking photos along the way.

Step Eight: Test it Out

There’s no better way to determine if you calibrated properly than to take a ride. Hit the road in your newly jetted bike and pay close attention to how it feels. Listen for popping or backfiring sounds, lean into the acceleration and idling behaviors, and test it out at all throttle positions. Of course, you can always check the spark plugs again and see if they’re coming out clean, black, or white. Continue checking and testing until you find the right fit for your ride. 

Here at Demon’s Cycle, we make it easy to get the parts you need and we have the resources and information that make maintaining and improving your bike simple. Explore our inventory of parts and upgrades and speak with our expert staff about taking your bike to the next level today.