Here’s Why Your Motorcycle Won’t Accelerate

Motorcycle Acceleration

You are on a road trip on a weekend after a taxing work week. You want to feel the rush of wind passing you as you accelerate your motorcycle to a top speed. But wait, your bike is not accelerating as you wish. Ugh…, frustrating isn’t it? Just when you think its only your boss that frustrates you.

Poor acceleration is frustrating. Your motorcycle will start losing power whenever you twist the throttle to accelerate. And this problem can persist in any gear.

So, why does motorcycle won’t accelerate? Poor acceleration problems are associated with the spark plugs not being in a healthy condition. The spark plugs have worn out or had gotten dirt into it to ignite the fuel mixture properly. Other possible reasons include 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

Spark plug is an essential component of your motorcycle as 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

Fractured insulator tip, bridging of electrode gap, or mechanical damage caused by a foreign object in the combustion chamber will result in a worn out and damaged spark plug.

A worn-out spark plug will not ignite the combustion chamber properly and this issue will cause poor acceleration in your motorcycle.

Solution: You need to follow the recommended maintenance schedule. Plugs may have been left in the engine for far too long. 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, it is damaged. You need to replace it with a new one. If you think the mechanical damage can be repaired, please give it a rest. It will cause the same problem again in few days. So changing your spark plug is the only option if it has worn out or suffered a damage.

Dirt/deposits in the spark plug

If your spark plug has dry sooty deposits encrusted on the side or center electrodes or both, then the carbon deposits, ash deposits and oil deposits have accumulated in your 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.

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

For the spark plugs, if the deposits are recent, it 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. 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.

Solution: Check for the correct plug heat range for your motorcycle and verify if you have the right type of spark plug or not. If the spark plug has eroded electrodes, you need to replace it with a new one anyway. Replace the existing with a correct type of spark plug in your engine.

Reason #2: Problems in Air flow

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.

Solution: First up, check your air filter. Are they clean enough for the air to enter? 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

Another reason for poor acceleration is because of insufficient fuel in the combustion chamber. When the air-fuel mixture is not to 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 into the combustion chamber:

  • 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.

Solution: Check your fuel levels in the meter to confirm there is sufficient petrol in your motorcycle. If it is not, well, go to the nearest gas station or petrol bunk to fill the fuel.

If there is enough fuel in the engine of your motorcycle, check for contamination in the fuel. This can be checked by the smoke coming out of the silencer. If the colour is grey, then you have filled up a contaminated fuel into the motorcycle fuel tank.

If the smoke does not give enough indication, another method is to remove the petrol 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 petrol.

Dirt in the Carburetor

Dirt in the carburetor can block the fuel flowing into the combustion chamber. Insufficient fuel in the system, as described earlier, will cause problems in starting the motorcycle as well as in accelerating.

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

Solution: Dirty carburettors are a headache. Cleaning the dirt in carb requires you to disassemble each and every part, cleaning them and then reassembling it back.

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 petrol or thinner to clean the carb. But a clean carburetor solution is a 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.

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

Solution: 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 in air entering the system, fuel entering the system or problems in spark plug.
  • Spark plug issues include worn-out or damaged spark plug, dirty spark plug and incorrect type of spark plug.
  • 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 petrol 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.