The motorcycle misfire is pretty apparent, and the sound of the engine misfire can easily be detected. But the majority of people don’t know what happens inside the engine during a misfire and what are the causes behind it and the early symptoms of a motorcycle misfire, if identified can prevent severe damage to the engine.
A motorcycle misfire is an event where the cylinder remains unfired because one or more strokes of the combustion cycle don’t occur. The prime reason for misfiring is caused by clogged/faulty fuel system or ignition system components. The motorcycle exhaust sound skips in an erratic pattern if the engine is misfiring.
In this article, we will understand what engine/motorcycle misfire is what it really means. Also, will discuss the major causes/reasons for motorcycle misfire and some early symptoms/signs you should look out for.
You will also know how to finally stop this engine misfiring issue and how to prevent it to avoid further headaches and money spent.
Table of Contents: (Click To Go To The Desired Section Of This Article)
What Is Motorcycle Misfire?
A motorcycle misfire is an unsuccessful completion of a full combustion cycle where either the intake, compression, power/combustion or exhaust stroke of the combustion process doesn’t take place and the cylinder remains unfired, resulting in motorcycle misfire.
During the combustion process, the air/fuel mixture gets inside the combustion chamber during the intake stroke. When the mixture gets inside it will get compressed by the piston so it’s called a compression stroke.
Once its fully compressed and the piston is at its TDC (top dead center position) the air/fuel mixture gets ignited by the spark plug’s flame front sending the piston down in the cylinder to transfer power from the connecting rod to the crankshaft and finally to the rear wheel, so it is called power/combustion stroke.
The leftover gases of the burned air/fuel mixture are then expelled from the combustion chamber to the exhaust through the exhaust valve, so it is called the exhaust stroke.
If any one of the combustion process’s strokes fails to occur, then the motorcycle’s engine will misfire.
To carry out a successful combustion cycle for a motorcycle to run properly these elements are needed whether it be a 2-stroke or a 4-stroke motorcycle.
The only difference is the intake, compression, power generation, and exhaust gas expulsion are done in only 2-stroke because the engine build in 2-stroke motorcycles is different from 4-stroke motorcycles.
What Does Misfire Mean In Motorcycle?
A motorcycle misfire simply means that the cylinder of the motorcycle remains unfired and does not complete an ideal full combustion cycle. This will result in motorcycle misfire where the bike will briefly stutter/stumble and lose RPMs (power) in an erratic manner.
You will experience your motorcycle will misfire on acceleration, and the exhaust sound will skip and go off rhythm for a few seconds.
The uneven supply of fuel & air or a poor ignition process will cause the motorcycle to lose power and will misfire under acceleration and even during idling.
Note: Most people get confused between misfire and sputtering, w during sputtering motorcycle’s engine is not able to achieve full combustion and performs a combustion cycle (intake, compression, power, & exhaust stroke) in a sub-optimal manner.
Whereas during a motorcycle misfire the cylinder remains unfired due to one of the strokes of the combustion cycle (intake, compression, power, & exhaust stroke) does not occur.
The effect of both sputtering and misfire will be the same as the motorcycle will momentarily lose rpm(power), and stutter/sputter but the damage from the misfire will be far greater due to the higher amount of pressure build-up inside the cylinder.
And a sputtering engine if left undiagnosed will later develop an engine misfire problem.
If you want to know if your motorcycle is sputtering and how to stop it, then please check out the article. ( Click The Underlined Link To Read )
What Are The Most Common Signs/Symptoms Of Motorcycle Misfire?
When your motorcycle is misfiring there are some obvious signs/symptoms you will notice.
These symptoms will get worse if ignored and will cause additional problems such as Engine Knocking or Backfiring. ( Click The Underlined Link To Read )
So here are the signs/symptoms of Motorcycle Misfire.
1. Motorcycle Exhaust Sound Skipping & Going Off-Rhythm
Motorcycle skipping (off-rhythm) exhaust sound is the ultimate clear-cut sign that you can spot when the motorcycle misfire.
A normal exhaust sound while revving or idling the motorcycle has a pattern because of a set firing order ( e.g. 270° – 360° crank). So when a motorcycle misfires the combustion timing misses and causes a skip in the exhaust sound.
2. Motorcycle Misfire During Acceleration & Idling
Motorcycle/bike misfire on acceleration or idling indicates that there is a malfunctioning fuel system or ignition system of the motorcycle.
During acceleration or even at idling the motorcycle needs a steady supply of air and fuel to have a successful combustion process.
Clogged/leakage to the fuel lines or air filter causes an imbalance in the air/fuel ratio supplied to the engine.
Or ineffective ignition caused by bad spark plugs or ignition coil will either not burn the fuel properly or cause a weak spark condition.
A faulty fuel system & ignition system will cause the engine misfire when you accelerate or idle your motorcycle.
3. Strong Smell Of Unburned Gas From Exhaust
During a combustion process, the air/fuel mixture gets ignited and the burned gases get expelled through the exhaust.
When the motorcycle misfire happens, a lot of fuel remains unburned and gets thrown out of the exhaust pipe. This unburned fuel emitting out of the exhaust is due to an engine misfire and has a strong smell to it.
So whenever your motorcycle misfires, there is a high chance you will experience a strong smell of gas while riding or idling your motorcycle.
4. Motorcycle Losing Power Frequently
A misfiring motorcycle faces issues such as uneven air/fuel supply and inefficient ignition of the fuel.
For a motorcycle to have a steady power output it needs to have an ideal full combustion cycle (intake, compression, power, & exhaust stroke) with a proper air/fuel ratio supplied to the combustion chamber and a good spark condition.
A misfiring motorcycle frequently loses power due to one of the strokes of the combustion cycle misses (do not take place) and the cylinder remains unfired, this causes the motorcycle to suddenly lose power while riding.
5. Motorcycle Frequently Stalling At Low Speed
In carburetor motorcycles, the pilot jet controls the fuel supply at idle and low speed. And in fuel-injected motorcycles, the fuel injector supplies the fuel.
Carbon and dirt build-up in the pilot jet or the nozzles of the fuel injector will disrupt the supply of fuel to the combustion chamber.
So the motorcycle will misfire and stall at low speed due to disruption to the fuel supply caused by a clog or leakage.
Keep a look out for some of these signs that will definitely help you in identifying motorcycle misfire also known as engine misfire.
Keep a look out for some of these signs that will definitely help you in identifying motorcycle misfire also known as engine misfire.
What Are The Most Common Reasons For Motorcycle Misfire?
Now we will look into some of the most common causes/reasons for motorcycle misfire.
And the majority of the reasons for a motorcycle misfire are caused by a malfunctioning/damaged fuel system, air supply/vacuum, or ignition system components, which either need a replacement or cleaning/servicing.
So here are the most common Reasons/Causes for Motorcycle Misfire.
1. Faulty Carburetor Or Fuel Injector
A faulty carburetor may include issues like clogged jets (main jet, pilot jet, needle jet) or out-of-tune air/fuel mixture is one of the top reasons for motorcycles to misfire.
For fuel-injected motorcycles, the injector itself being clogged ( spray nozzles) by carbon build-up or dirt will restrict the flow of the fuel to the combustion chamber.
Restriction of fuel being supplied to the combustion chamber will cause an imbalance in the air/fuel ratio which will affect the combustion process resulting in motorcycle misfire.
2. Bad Spark Plugs/Spark Plug Wires
To ignite the air/fuel mixture a spark plug in good working condition is essential.
Bad spark plugs will fail to ignite the fuel in the combustion chamber and if they did will result in a weak spark condition which is not ideal for a robust combustion process.
A bad spark plug will not fire or completely miss the igniting timing of the fuel, which will result in a misfire.
The spark plug wire carries the electric current to the spark plugs which is needed to ignite the fuel. The insulation layer of the wires can crack or burn if coming into contact with a hot surface and can also detach the wire from the spark plugs due to heavy vibrations.
This can cause failure in carrying current to the spark plugs which is needed to ignite the air/fuel mixture, so a worn/damaged spark plug wire can also cause the motorcycle to misfire.
3. Worn Ignition Coil
An ignition coil is one of the most components of the ignition system of the motorcycle which helps to convert the battery voltage of 12.7-13.6 volts into 20,000-50,000 volts, which is required to ignite the air/fuel mixture in the combustion chamber.
A worn or damaged ignition coil will fail to transform and carry the current to the spark plugs, which will result in a motorcycle engine misfire.
4. Clogged Air Filter
Clogging of the air filter can be caused by a dirt/debris build-up over time and sometimes it just needs a cleaning service or straight-up replacement.
Either in both cases, a clogged air filter will exponentially decrease the amount of air supplied to the engine’s combustion chamber.
The ratio of air and fuel will get imbalanced significantly and will cause obstacles during the ignition of the air/fuel mixture.
So a clogged air filter will play a significant role and is one of the major reasons behind a motorcycle’s engine misfiring.
5. Damaged Fuel Pump/Fuel Line
For a motorcycle to run it needs fuel, a fuel pump, fuel line/fuel return line
will carry and supply the fuel from the tank to the combustion chamber through a carburetor or fuel injector.
Damage or leakage to the fuel pump and fuel lines will completely stop or significantly decrease the amount of fuel transferred to the engine for successful combustion.
A damaged fuel pump/fuel line will cause an imbalance in the air/fuel ratio and cause problems in the ignition procedure which will result in motorcycle misfiring.
6. Vacuum Leak/Compression Loss
When the pistons move up and down during a combustion cycle, the cylinder and combustion chamber has a particular amount of compression buildup in it, which helps in igniting the air/fuel mixture and carrying on the combustion process.
Vacuum leaks in a motorcycle caused by a blown head gasket, leaking valves, and intake manifolds will introduce an extra amount of external atmospheric air into the air/fuel mixture.
If you want to know how to spot a blown head gasket and what are the causes behind it and how to fix it quickly then please check out the article. ( Click The Underlined Link To Read )
This will cause a severe imbalance in the air/fuel ratio where the ignition of the fuel will not be optimal and the motorcycle misfire issue will take place.
How To Stop & Fix Motorcycle Misfire?
To stop a motorcycle misfire and fix it in an appropriate procedure, replace the severely worn/damaged components of the air supply unit, fuel system, & ignition system of the motorcycle.
Vacuum leaks caused by blown gaskets and rubber lines of the intake manifold should be replaced as soon as possible.
Worn or Damaged components of the Fuel and ignition system such as the fuel pump, fuel lines, carburetor, fuel injector, ignition coil, spark plug wire, and spark plugs should be replaced for a motorcycle to run properly and stop misfiring.
A damaged air filter should also be replaced to maintain a correct air/fuel ratio.
How To Prevent Motorcycle Misfire?
To prevent a motorcycle misfire, regular maintenance/servicing checkups of the fuel system & ignition system components are necessary. Cleaning carbon buildup and dirt from these components will allow the motorcycle to have an optimal combustion cycle and better performance.
The fuel and ignition system components as discussed earlier in this article along with the air supply unit of the motorcycle should be maintained and cleaned from time to time.
For example, carbon buildup on spark plugs will poorly affect the flame front/spark of the spark plugs which is needed to ignite the air/fuel mixture.
Clog or dirt accumulation in the air filter will cause restrictions in the air-supplying process which will cause an imbalance in the air/fuel ratio. This will result in the motorcycle running a highly rich mixture, a lot of unburned gas, and the infamous motorcycle misfire.
So a maintenance routine of the air system, fuel system, and ignition system of the motorcycle will prevent motorcycle misfire.
Most Common Motorcycle Misfire FAQ
Is engine misfire serious?
An engine misfire is a serious scenario for your motorcycle where it can lead to permanent damage to the internal parts of the engine.
Is an engine misfire expensive to fix?
Generally fixing an engine misfire will cost you around $100-$1000 USD depending on the replacement or repair cost of the fuel system, ignition system, and air supply system of the motorcycle.
