Why Does My Motorcycle Not Accelerate?

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Many bike lovers buy motorcycles for the love of high speeds. For one to move from a standby position to get to high speeds, the bike needs to accelerate. To do this, the rider is required to turn the throttle.

In most instances, you may turn the throttle to make the bike accelerate, and it does. In other instances, the bike may fail to accelerate. The failure/hesitation of the bike to accelerate may be caused by a wide range of reasons.

Acceleration System of a Motorcycle

Before we get to why your bike is not accelerating, let us look at a bike’s accelerating system. In motorcycles, almost everything is operated using the handlebar. For instance, the handlebar acts as a steering control.

The handlebar also has various buttons, each of which performs different roles. Furthermore, the right end of a motorcycle can be turned to bring about acceleration.

In most scenarios, it is referred to as the throttle. Now, this is what we are going to base our focus on when explaining the acceleration of bikes.

The throttle is normally connected to the engine through a cable known as the throttle cable. When you accelerate your bike, the throttle cable causes the butterfly valve to open.

The more one accelerates, the more this particular valve opens up. While doing this, air and fuel from the carburetor flow to this valve.

A carburetor is a device in motorcycles that is responsible for the proper mixing of air and fuel. It is this mixture that causes the bike to move. However, before it actually moves, combustion must take place.

The part of a bike that is responsible for causing combustion is a spark plug. The spark plug does this by igniting the air and fuel mixture, which then causes the pistons it move down.

The pistons are connected to the crankshaft, making the gears turn which is attached to the bike’s chain. The bike’s chain is connected to the wheel; as a result a bike’s wheel usually moves in accordance with its chain.

This interconnected system is what causes the bike to move faster. Basically, with every turn of the throttle, this entire process happens more rapidly. This then causes increased bike speeds, commonly known as acceleration.

Cause of Motorcycle not Accelerating

Knowing how the acceleration system works helps you understand the causes easily. In essence, in the event that you notice the bike is not accelerating, you will know where to start.

All in all, let us look at the common reasons as to why your bike is not accelerating.

Worn Out or Dirty Spark Plugs

When your bike is not accelerating, one of the reasons could be that the spark plugs are worn out. Basically, the plugs have lost their effectiveness in causing a spark.

When this happens, they are unable to cause an ignition. If there is no ignition, the bike does not accelerate.

In other instances, the spark plug’s condition may be in great shape, but it is filled with dirt. Most of the time, you will find that carbon and oil residues have built-up in the spark plug electrodes.

This, in turn, affects its ability to ignite air and fuel. If the ignition is affected, so is the acceleration of the bike.

Faulty/Broken Carburetor Spring

The carburetor spring is a small but very integral part of a motorcycle. It is so important that when it has any malfunction, the bike’s overall performance is affected. Let us break this down for you.

The carburetor spring is located where the throttle cable joins the carburetor. The carburetor spring usually controls the opening of the butterfly valve.

Remember, the butterfly valve is integral in facilitating your bike’s acceleration.

In the event that this spring is broken/spoilt, it will not open the butterfly valve. If the valve does not open, air does not rush in.

This then causes the bike to have a lot of fuel in the engine and not enough air to mix with it. It is this improper mixture of air and fuel that hinders acceleration.

Dirty Carburetor

A dirty carburetor could also cause your motorcycle not to accelerate. In essence, when the passage and jets in the carburetor are clogged with dirt, air and fuel do not move freely.

If these two fluids are unable to move into the engine properly, there is improper supply. In turn, the bike does not accelerate because combustion will not take place as it should.

Issues with the Throttle Cable

The throttle cable usually connects the engine (carburetor) and the throttle. It is integral in the functioning of the bike as it plays various roles. One, it determines how wide the butterfly valve needs to open.

It is also in charge of controlling the times in which it is supposed to be closed or opened. All of these depend largely on how fast or slow you as the rider want to go.

When the throttle cable has issues, it translates to poor or no acceleration at all. One of the throttle cable issues that can cause this is excess slack. When the cable has excess slack, it does not give the butterfly valve a full pull.

This then results in the improper opening of the butterfly valve. Improper opening of the butterfly valve results in uneven mixing of air and fuel. This is what makes the bike unable to accelerate.

How to Fix a Motorcycle Which Wont Accelerate?

There are few things you can do to fix a motorcycle that does not accelerate:

Consult a Mechanic (Worn Out/Dirty Spark Plugs)

If you feel like your bike’s spark plugs are worn out, consult a mechanic. The same goes when the bike’s failure to accelerate is caused by dirty spark plugs. A mechanic will examine the plugs and advise you on the way forward.

If the mechanic finds a problem there, the most definite choice would be to replace them with new ones. If he/she feels like they are in good condition and just dirty, he/she will clean them for you.

Replace the Carburetor Spring (Faulty/Broken Carburetor Spring)

There is a good chance that the acceleration issues of your bike are as a result of a broken carburetor spring. Before actually coming to this conclusion, it is good that you run a quick diagnostic test to be sure. One way of confirming this by following these few steps;

  1. Turn off the bike.
  2. Remove the airbox.
  3. You then turn the throttle as you look through to the carburetor. As you do this, your focus should be on the butterfly valve. If you notice that it does not open, then you know that the spring is faulty.

The next cause of action at this stage is to replace the spring.

Clean Your Motorcycle Carburetor (Dirty Carburetor)

If you notice that your bike is not accelerating, maybe it is because your carburetor is dirty. The best thing to do is clean the carburetor. The first thing that you need to do here is to collect the right tools and supplies.

Here you will need a flat and a Philips screwdriver. You will also need needle-nose pliers, a socket set and a wire brush. Cleaning supplies needed here are a carburetor and choke cleaner and a gasket set.


  1. Take out the carburetor and the float.
  2. Remove the jets and outer parts.
  3. Once you have removed everything listed here, you start cleaning them. The supplies will come in handy in this step.
  4. After you are done cleaning, put back each of these items starting with the jets.
  5. You then put back the outer parts and then the float.
  6. The last part involves putting back the carburetor.

If you know you do not know how to clean a carburetor, do not do it. Just take it to someone who will do it for you properly.

Tightening the Nut above the Knob (Issues with the Throttle Cable)

For you to fix throttle cable issues, you need to first examine it. You can do this by turning the throttle when the bike is off and examining the butterfly valves.

If these valves do not open with a full-throttle twist then, there are high chances the cable has an issue. In most cases, it has an extra slack.

You can fix this by tightening the nut that is above the knob connecting the carburetor and the end of the cable. In as much as tightening is a solution to most bikes with such issues, it does not fix these issues in older bikes.

Basically, in older bikes, the throttle cable usually stretches. Therefore tightening the nut will have no effect at all.  The only option one has in such an instance is to replace the throttle cable with a new one.


Turning the throttle and accelerating your bike on the highway is simply amazing. Hence in case your bike does accelerate when you instruct it to, you can get frustrated. There are various reasons that may cause this.

Sometimes, it may be because the carburetor is dirty. In other instances, it may be due to excess slack in the throttle cable. It may even be caused by faulty carburettor spring or worn-out spark plugs.

Whatever the case, it is important to run a diagnostic test first and find the root. If you can fix the issues yourself, do it. If you cannot fix the issue, consult a mechanic.

Josh Berry - MotoShark Editor
Josh Berry
I'm a off-road enthusiast, extreme sport fan and the editor of MotoShark. If you have any questions or suggestions regarding this article, please leave a comment or contact me.

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