Motorcycle Stutter When Accelerating? Here’s Why (SOLVED)

It’s springtime and everybody’s firing up their bikes and getting ready for riding season.

After sitting for a while, lots of people like to take the bike out for a short, fast rip to make sure everything is working in tiptop shape.

So, you pull out onto the highway to gun it up, but the bike stutters whenever you try to accelerate! Let’s dig into the issue and find you a solution, so your riding months are as fun as can be!

Why Does My Motorcycle Stutter When Accelerating?

There is a point in any motorcycle’s life when proper acceleration is negatively affected by sputtering. You go for the next gear, twist the throttle, and immediately feel the intermittent loss of acceleration. This can happen for one of several reasons. 

Most often, you are experiencing an issue with your carburetor. An improperly tuned or dirty carburetor, as well as fuel or vacuum leaks, can cause the stutter.

Alternately, the stuttering can be caused by problems with your ignition system. Ignition system problems that cause stuttering can be the result of cracked or dirty spark plugs, faulty spark plug wires, or a failed ignition coil. 

Carburetor issues generally create improper air-to-fuel ratios, while ignition issues are going to be preventing your bike from creating the spark needed for acceleration.

All gasoline engine vehicles need spark, air, and fuel to operate. If one of those three things is absent or delivered at the improper ratio, your motorcycle will sputter when accelerating.

So let’s take a deeper look at the issues causing this sputtering so we can troubleshoot your issue and get you rolling on the road in no time!

1. Carburetor Issues

A carburetor is a mechanism that correctly mixes fuel and air to the combustion chamber via the intake valve. The correct amount of fuel, when mixed with the right amount of roaring air, atomizes, creating a fuel vapor that is easier to ignite in the combustion chamber than liquid fuel.

If the carburetor is dirty or adjusted incorrectly, or if the jets are clogged, it won’t mix the fuel and air properly to create the fuel vapor to combust properly. A vacuum leak can reduce the amount of air getting to the combustion chamber. If you have a fuel leak, your engine won’t be getting enough fuel.

2. Dirty Carburetor

Certain components of the carburetor can become ineffective if they are gummed up or clogged with dirt, dust, or debris. The carburetor relies on meticulously placed voids and valves to direct the air and fuel. If debris collects around the valves, they can stick open or shut. 

Inside the carburetor, the fuel passes through tiny holes in the center of the fuel jets to ensure the proper amount of gas passes up to the airflow so it can mix and atomize.

If the jets become clogged with any kind of dirt or grit, there won’t be enough fuel passing through them.

Airflow issues can be diagnosed by checking your vacuum lines on either side of the carburetor. If you find any wear on your air intake or vacuum lines, they need to be replaced.

Vacuum seals on either side of the carburetor can become brittle and crack over time, leaking air into a space that needs only a specific amount.

If it is a fuel issue, check for a fuel leak in any of the fuel lines.

Improper delivery of fuel will definitely cause your motorcycle to stutter when you are accelerating. This is because too much air and not enough fuel vapor are entering the combustion chamber and causing weaker combustion.

If the jets between the float chamber and air chamber are clogged, you’ll need to remove the float chamber to get to the jets.

Once you can clean the jets, use carburetor cleaner and maybe a bit of compressed air to make sure they unclog. If there is any grit or debris left, use a needle to carefully clear the jets.

Related: 6 Reasons Motorcycles Can Shut Off While Riding (Explained)

3. Air/Fuel Adjustment

Because carburetors are so delicate, the air/fuel mixture can be adjusted. This is done by carefully turning the air/fuel adjustment screw on the carburetor body. This will either add or reduce fuel in the mixture. 

If you are running too rich, you’ll need to adjust the screw to reduce the amount of fuel in the mixture. If the opposite is true and you are running on a lean fuel mixture, then you need to adjust the screw to get more fuel running into the mix.

If your bike is running rich or lean, there will be noticeable build-up on the insulator tip. This build-up will affect the ignition system.

4. Air Filter

A clogged air filter can easily cause your bike to stutter during acceleration because it is preventing enough air from entering the carburetor.

If the clogged filter doesn’t let in enough air or lets it in inconsistently, it will cause stuttering problems.

Removing and replacing a clogged air filter can immediately improve your stuttering issue and the performance of the bike. It’s easy to do and a cheap remedy. 

If you have some distance to go before you can replace the filter, you can try blowing compressed air all around the filter to remove dust and dirt. This will be a temporary solution and you should replace the air filter as soon as possible.

5. Ignition System Problems

The ignition system provides the spark that combusts the vaporized fuel in the combustion chamber.

Without a consistent spark, the bike will stutter when accelerating. There are several pieces that, if faulty, will keep the combustion chamber bogged down with too much fuel.

Related: Has My Motorcycle Starter Relay Gone Bad? (Explained)

6. Spark Plugs

Spark plugs seat on top of the combustion chamber and create the spark that causes the timely explosions that make your pistons fire. The combustion chamber must have the exact amount of vaporized fuel to create the right amount of energy. 

If the spark plugs are corroded, broken, or have too much build-up on the insulator tip, they will not fire properly, and create the stutter when you’re chomping down on your throttle.

To check your spark plugs, make sure the bike is off and remove the rubber spark plug caps. Using the correct size spark plug socket, carefully remove the spark plugs to look at the insulator tips. 

If the spark plugs are warped or the ceramic element is cracked, simply replace the spark plugs with new ones.

If the spark plug insulator tip is sufficiently covered in build-up, it won’t be creating the proper amount of spark for combustion and will also need to be changed out for new ones.

One way to know about your air/fuel mixture is the color of the build-up on the insulator tips.

If it looks blacked or like charcoal, you are running too much fuel. If the metal of the insulator tip is covered in a white, chalky buildup, you are running too lean. This can be adjusted at the carburetor and will keep the bike from having ignition issues causing the stuttering when you accelerate.

7. Spark Plug Wires

The spark plug wires move the electricity to the spark plugs, allowing them to fire.

If your spark plug boots, casing, or wiring are damaged, they may not be conveying the right amount of current to the spark plugs. This can be the cause of your bike’s stuttering issues during acceleration.

Upon inspecting the wire, if you find they are damaged, then you will need to replace them. 

This should solve some, if not all, of the stuttering.

8. Ignition Coil

The ignition coil creates the high voltage needed to produce the spark required for combustion. If the spark plugs or spark plug wires are faulty, it can lead to the untimely demise of the ignition coil. 

Common symptoms of a bad ignition coil include loss of power, backfiring, misfiring, stuttering, and vibrating. If you still find yourself stuttering while accelerating, and you’ve checked the carburetor issues, spark plugs, and spark plug wires, there’s a good chance your ignition coil is bad. 

To test for a bad ignition coil, you’ll need a voltmeter or multimeter that can measure Ohms. Remove the pigtail for the primary side of the coil and test it- you should be within the approximate range of 3-5 Ohms. 

Next, test the secondary end of the coil. Keeping one lead on the primary side, put the other lead in the plug wire. It should read in at around 10,000 Ohms. 

If either of your readings is out of the acceptable range, you’ll want to replace that ignition coil.

9. Engine Timing Issues

It is less likely, in the event of stuttering while accelerating, that you are having timing issues, but it is a possibility. If you have looked over the carburetor, airflow system, and ignition system, but still have the stuttering problem, it could be a larger problem. 

Engine timing issues are often due to valves timing being off and can have terrible consequences. If you are stuttering while accelerating and none of the aforementioned issues are present, have your engine looked at by a trusted professional.

If you are bouncing around on a V-Twin, this problem may be more commonplace than with other motors. 

Because timing issues can necessitate an expensive fix, inspect all the issues above before you spend a lot of money on cracking open the engine.

10. Stuttering Problems In Fuel Injected Systems

Most of the issues we’ve covered in this article pertain to carbureted bikes. If your bike is newer, it employs fuel injectors instead of a carburetor. Fuel injectors are much more efficient. 

Because the air-to-fuel mixture is regulated differently, there’s a good chance your stuttering problem comes from either the fuel pump or the fuel filter.

You will want to examine the problem by completing a fuel flow test. A fuel flow test is the best way to determine if the issue originates at the fuel pump or the fuel filter because it tests both simultaneously.

Related: Motorcycle Idles But Won’t Accelerate (Solved & Explained)

We Hope You’ve Discovered Why Your Bike Stutters When Accelerating

The best part about these examples and solutions is that they are relatively simple and someone with little mechanical knowledge can do most of them.

The carburetor and ignition issues are fairly simple to diagnose and fix, but the engine timing issues will need a much higher level of technical knowledge. We recommend you always have a certified mechanic look at internal issues like valve problems. 

Sources | Why Is My Motorcycle Bogging On Acceleration | How Do Motorcycle Carburetors Work?

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