Motorcycle Won’t Accelerate? Here’s Why!

A guy riding a motorcycle on a beautiful road - throttle won't accelerate

I was on a road trip on a weekend after a taxing work week. After a few miles on the road, lo and behold, my motorcycle won’t accelerate well.

Not gonna lie, it was a frustrating road trip!

Just when I think it’s only my boss that frustrates the heck out of me.

Bad trip aside. Poor acceleration is annoying. Your motorcycle will start losing power whenever you twist the throttle to accelerate.

And the worst part:

This problem can persist in any gear. Even at higher gears.

So, why won’t a motorcycle accelerate? Poor acceleration problems are associated with poor spark plugs. The spark plugs have worn out or have too much dirt to ignite the fuel mixture properly. Other possible reasons include a clogged carburetor or dirt in the air filter.

In order to run your motorcycle smoothly, you need your air flow, fuel flow and the spark plug to ignite the engine in its proper condition.

Any issues in one of these will create problems in the form of poor acceleration or the motorcycle running only on choke.

Without further ado, let’s look into each of the possible causes and the solutions.

Reason #1: Problems in Spark Plug

4 spark plugs

Spark plug is an essential component in a motorcycle.

It ignites the engine to power up your motorcycle to run. Any issues in the spark plug will eventually result in starting problems or acceleration problems.

Here are the typical spark plug concerns:

  • Spark plug has worn out
  • Dirt in the spark plug
  • Incorrect type of spark plugs in the engine

Spark plug has worn out

The sparkplug can be damaged or worn-out because of several reasons.

Major reasons include:

  • fractured insulator tip
  • bridging of electrode gap
  • mechanical damage caused by a foreign object
  • natural wear over its lifetime

No matter the reason, the consequence is the same.

Spark plug with center electrode tip worn out

A worn-out spark plug will not ignite the fuel in the combustion chamber properly. And in turn, this will cause poor acceleration in the motorcycle.


Follow the recommended maintenance schedule.

The spark plug may have been left in the engine for far too long. Without much inspection and checks.

If the damage is because of a foreign object in the combustion chamber, you need to remove that object before it causes damage to the cylinder and piston.

Coming to the spark plug. If it is damaged, you need to replace it with a new one.

Spark Plug

If you think the mechanical damage can be repaired, please give it a rest. It will cause the same problem again in a few days.

So changing your spark plug is the only option if it has worn out or suffered damage.

Dirt/deposits in the spark plug

If your spark plug has sooty deposits encrusted on the side or center electrodes or both, then there is deposit formation.

One of the carbon deposits, ash deposits, and oil deposits has accumulated in your spark plug.

Ash deposits on spark plug

Excessive amounts of deposits, be it in the form of carbon, ash or oil deposit, will form an outer layer on the spark.

As a result, the spark is masked to prevent ignition in the motorcycle engine. This will cause misfiring and hesitation during acceleration.


If excessive deposits have accumulated in a short span of time, then you need to install new valve guide seals to prevent oil slippage and ash deposits into the combustion chambers.

For the spark plugs, if the deposits are recent, they can be cleaned off from the electrodes so that the spark is no more masked.

However, if it has been a long time and the deposits have accumulated strongly, you need to replace it with a new spark plug.

Incorrect type of spark plugs in the engine

For each engine specification, there is a defined heat range for the spark plug.

Spark plug optimum heat range - infographic

If the spark plug does not withstand the heat and lies outside the specified heat range, you are going to get a blistered insulator and eroded electrodes in the spark plug.


Check for the correct plug heat range for your motorcycle and verify if you have the right type of spark plug or not.

Here is a thumb rule you can follow:

Reason #2: Problems in Air flow

Motorcycle Air Filter - red in color

Although the number of cases with issues in the airflow to the engine are low, it is better to check them just to be sure.

Here, the air-fuel mixture entering the engine is important for the motorcycle to run.

So, if the air entering the engine is not sufficient enough, then we have the problem of our motorcycle not getting enough power to accelerate despite you twisting the throttle to its maximum.

In other cases, the bike starts spluttering and eventually comes to a halt.

For this exact reason we need to check our air filter.

Air filter is not clean

You need to make sure that the air filter is clean.

If you feel there is too much dirt in the filter and not sufficient air is entering the engine, then insufficient air in the combustion chamber is causing your motorcycle to not accelerate properly.

Air filter and carburetor


First up, check your air filter.

Is the air filter clean enough for the air to enter? Or is it blackened?

Clogged air filters will cause starting and accelerating issues in the motorcycles.

If air filter is clogged, then it is time to remove the dirt accumulated and clean the filter.

Another better option, if there is too much dirt and it has been a long time, change the filter to a new one.

Reason #3: Problems in Fuel flow

Motorcycle Engine

Another reason for poor acceleration is because of insufficient fuel in the engine combustion chamber.

When the air-fuel mixture is not at the optimum levels, the motorcycle will not power up enough to accelerate. The fuel is not supplying high power after the combustion.

Here are the causes for problems in fuel flow:

  • Insufficient or contaminated fuel
  • Dirt in the carburetor
  • Damaged carburetor spring

Insufficient or contaminated fuel

If you have insufficient fuel in the engine or the quality of fuel is not good, then the acceleration problem is because of your fuel.

Good thing here is this problem is the easiest to fix.


Check your fuel levels in the fuel gauge to confirm there is sufficient gas in your motorcycle.

Motorcycle fuel gauge - low fuel level

If it is not, well, go to the nearest gas station or fuel pump to fill the fuel.

If there is enough fuel in the engine, check for contamination in the fuel.

This can be checked by the smoke coming out of the silencer. If the color is grey, then you have filled up contaminated fuel into the motorcycle fuel tank.

Smoke from motorcycle exhaust

If the smoke does not give enough indication, another method is to remove the fuel pipe which is connected to the carburetor, and collect the fuel in a clear bottle.

Upon seeing the collected fuel in a transparent and clear container, you will get to know whether the fuel is contaminated or not. 

Once you confirm the contamination, remove the fuel completely through the fuel pipe and refill with a better quality gasoline.

Dirt in the Carburetor

Dirt in the carburetor can block the fuel flowing into the engine combustion chamber.

Insufficient fuel in the system, as described earlier, will cause problems in starting the motorcycle as well as in accelerating.

Motorcycle carburetor

Clogged pilot jets blocking sufficient fuel flow, dirt in the petcock, clogged fuel lines, and dirty fuel filters are all possible causes that need to be checked in the carburetor.


Dirty carburetors are a headache.

Cleaning the dirt in carb requires you to disassemble each and every part, clean them, and then reassemble it back.

A man fitting carburetor in a motorcycle

For tips on cleaning the carburetor, check out our post here.

You need to be gentle while cleaning the pilot jets and fuel lines. Make sure to not scratch or damage the inner lines.

Also, most people use gasoline or thinner to clean the carb. But a clean carburetor solution is the preferred option if you are the one cleaning it yourself.

Damaged carburetor spring

If the spring in your carburetor is broken, then the air fuel mixture is not entering properly into the combustion chamber. The springs are located where the throttle cable connects with the carburetor.

Motorcycle Carburetor

Any problem in the springs will, as a result, cause acceleration problems in your motorcycle.


You need to take off your carburetor to replace the spring.

Disassemble the carburetor parts, replace the broken spring with a new one. It won’t be too difficult to replace if you have experience in cleaning your carburetor.


Here is a quick summary of the post.

  • The reasons why your motorcycle is not accelerating is because of problems with the air entering the system, fuel entering the system, or problems in the spark plug.
  • Spark plug issues include worn-out or damaged spark plugs, dirty spark plugs, and incorrect type of spark plugs.
  • For damaged and incorrect spark plugs, you need to replace them with a new one. For dirty spark plugs, if the deposits are recent ones you can clean them else you have to replace here too.
  • Air flow problems are because of a clogged air filter. If there is too much dirt on the filter, you need to either clean them or change the filter completely.
  • Fuel flow problems can be caused by insufficient or contaminated fuel, dirt in the carburetor or broken spring in the carburetor.
  • Insufficient or contaminated fuel is easy to fix by injecting the right fuel into the engine. You need to empty out the existing fuel through fuel pipe if the fuel is of deteriorated quality.
  • Dirt in the carburetor and broken spring requires you to disassemble the carb and fixing it up. If you don’t have experience in cleaning your carburetor before, fix this up with the help of a mechanic.