Motorcycle Engine Sounds Rough? 11 Typical Reasons (Explained)

One of the simplest pleasures of motorcycle riding is the sweet sound of a crisp motorcycle engine puttering along in the wind.

However, a rough-running motorcycle engine adds insults to an injury. Not only is a rough-sounding engine indicative of a mechanical problem, but it also interferes with the state of your ride.

This article lists some of the typical reasons a motorcycle engine sounds rough.

 

1. The Air Intake Filter Is Blocked With Debris

Your motorcycle’s airbox filter purges the incoming air of any dirt, dust, sand, or water debris to prevent its mixture with your air-fuel mix. This is why you need to clean or change these filters more often.

If your bike’s air intake filter is with dirt and debris, the amount of air required for typical ignition can’t pass through the filter. As such, it could harm your motorcycle’s idle and cause your RPMs to advance and delay.

2. Cam or Crank Position Sensor is Failing

Modern motorcycles have their ignition timing and air/fuel mix distribution performed by their ECU (Electronic Computer Sensor).

The ECU communicates with sensors throughout your bike’s electronic system to monitor the bike’s vitals and adjust ignition and air/fuel flow accordingly.

One of these sensors monitors your motorcycle’s crank or cam position and either advances or delays your ignition timing to compensate for angle shifts.

Suppose the cam position or angle sensor fails, or the connection between it and the ECU is interrupted, your ignition timing will adjust for no reason, and your motorcycle engine will pop, slap, and sound rough.

On this note, make sure you check 5 reasons a motorcycle makes a whining noise.

3. Bad Cam Chain Tuning

Your cam chain is responsible for keeping your bike’s engine timing consistent. Like all mechanical chains, your cam chain eventually wears out.

Over time, the cam chain’s metal expands and retracts until it can’t retain its spec tension. Once its pressure is compromised, your engine timing falters, causing it to run poorly and generate abrasive clanking sounds coming from the engine.

• Cam chain wear causes incorrect valve timing, which is one of the most common causes of engine running problems.
• A worn or improperly tuned or tightened cam chain affects your air intake and exhaust system, reducing engine compression and causing your revs to fluctuate.
• The result is a motorcycle engine that makes some pretty harsh sounds.

4. The fuel Tank Filter is Blocked With Deposits

If the filter gets clogged, the fuel’s flow is restricted, and the fuel supply starts to run lean on power, allowing too much air to enter your bike’s combustion chamber.

The excess air can cause engine overheating, RPM lags, rough engine performance, and harsh motor noises.

• While some bikes are equipped with external fuel filters for easier maintenance, most bikes store the fuel filter in the bike’s tank.
• The fuel filter filters dirt, water, and rust deposits from your fuel before it leaves the tank and enters the injection system.

If your fuel is corrupted or contaminated, or if your filter isn’t inspected, cleaned, or changed per the service spec in your manual, your motorcycle’s fuel supply is blocked. When this happens, the engine will make rough sounds while riding.

5. Running Your Motorcycle With Low Oil Levels or Contaminated Oil

One of the most common reasons a motorcycle engine sounds rough is because of a low oil supply or the use of expired or improper oil.

Motorcycle engines and transmissions comprise various moving metal parts in proximity to one another. In fact, many of these parts come in contact with one another.

If your motorcycle is running low on oil, or if the oil is degraded and needs to be changed, you’ll notice grinding noises coming from your gearbox and engine. At this point, your engine will make rough sounds. And if left unchecked, the engine will overheat.

Finally, there are different grades and mineral types of oil, like the synthetic, semi-synthetic, and pure mineral oil.

Different motorcycles use different engine types, and the oil required for optimal operation varies from motor to motor. Using the wrong grade of oil can cause your motorcycle engine to sound rough and deliver decrease performance.

6. Vacuum Leak in Air Intake

If your motorcycle’s air intake system develops a vacuum leak in its components, your air/fuel mixture will run rich in fuel and low on air. Running rich means that the fuel fills the space, in your combustion chamber, created by the interference in your air supply.

That said, vacuum leaks most commonly form in your air intake boots as cracks form around it. It could also form in worn-out carb gaskets.

Not only do these leaks allow air to flow where it doesn’t belong, but they also let it escape areas where airflow is required for essential processes like ignition and idling.

Regardless of where the leak comes from, once formed, vacuum leaks create pressure loss, impairing your motorcycle’s engine compression and causing it to sound rough.

Here’s how to find out if a vacuum leak is a reason your motorcycle engine is making harsh noises:

1. Inspect your air intake boots and see if they’re worn, cracked, flexible, or flaky.
2. Next, inspect the hose clamps around those intake boots to ensure they’re not letting any air in. It may be as simple as replacing the air intake boots.
3. Examine the various gaskets throughout your air intake system. It must be airtight and in good condition to keep the air out.
4. If any of your intake seals seem broken, the air is allowed to escape, altering the compression and air supply and harming your bike’s RPM consistency.
5. Some bikes have a vacuum port that runs from the top of the engine to the carb. Sometimes these hoses leak.
6. Some bikes have an extra hose for accessories or add-ons. If so, unused hoses must be capped off, or air can escape, and your idling will suffer.

7. Faulty Spark Plug Wires or Ignition Coils

Before inspecting the spark plugs themselves, we suggest considering the conditions of your motorcycle’s ignition coil, coil packs, and spark plug wires. If these components are burned out, replacing them will only be a temporary solution.

• An integrated network of spark plug wires, ignition coils, and coil packs powers your bike’s spark plugs.
• This ignition coil network sends a powerful voltage to the spark plug, initiating a vital spark that clears the spark plug’s gap.
• The ignition coil and plug wires on your motorcycle burn out at different rates, driving the spark they render to become irregular.
• An irregular spark causes sporadic engine RPMs, developing the coarse engine and idling noises.

Ignition coils, coil packs, and spark plug wires are most frequently worn out from heavy use, unsuitable storage, or riding in extreme weather.

Regardless of the cause, if your ignition system can’t generate enough volts to create a spark that can cross the spark plug gap and ignite the combustion process in your engine, your motorcycle engine will run and sound noticeably rougher than usual.

8. Spark Plugs Need To Be Changed

Spark plugs are responsible for sparking your motorcycle’s ignition system into action.

The charge induced by the spark plug ignites the air-fuel mixture inside the combustion chamber, powering your engine’s pistons.

Spark plugs get repeatedly shocked during everyday use until they eventually burn out. Running your motorcycle on worn spark plugs affects engine performance and causes your idle to sound rough.

Here’s how to inspect your spark plugs on a motorcycle with a rough idle:

• If the firing tip of the spark plug is tan or grey, your spark is clearing the plug’s gap, and your ignition is in working order.
• Dry black spark plug tips mean the spark is weak, and your idle may be affected (caused by a rich fuel mix).
• Wet oil residue on your spark plug tips means a weak spark and idle may be affected. This often results from worn piston rings, letting oil pass.
• Scorched white plug tips mean the spark is weak, and your motorcycle may idle rough. It is usually caused by overheated engine or faulty ignition coils.

 

Learn more about this by reading our article on what to do when a motorcycle idles rough.

9. Fuel Injectors are Stopped Up

Modern motorcycles use Fuel Injection systems to inject fuel into the engine’s combustion chamber.

The fuel injectors are controlled by an electronic computer unit, or ECU, which communicates with a system of sensors to adjust the fuel supply and ignition timing appropriately to the bike’s running conditions.

An unkept motorcycle or fuel system can develop corrosion, moisture, and mineral deposits that can clog your injectors as the corrupted fuel passes through.

If your motorcycle’s fuel injectors are clogged by rust or lousy fuel, your bike will run lean on power, and your engine will start running and sounding rough.

10. Carburetor Is Compromised, Clogged, or Worn Out

If your bike’s carburetor is rusted, jammed, damaged, or unkept, your fuel supply will run lean on fuel, and your motorcycle engine will start sounding rough.

The carb is responsible for supplying your motorcycle with fuel on the bike without a fuel injection.

A mechanical bowl and a float needle system regulate the fuel supply. The needle rises as the bowl fills, ensuring that the fuel supply is shut off once the carburetor bowl is filled with the proper amount of fuel.

If the carburetor issues interfere with fuel flow, the air-fuel mix is thrown off its spec ratio.

Thus, if a corrupted carburetor is why your bike’s engine sounds strange, you’ll need to rebuild the carburetor. To do this,

1. pull the carb,
2. disassemble it,
3. clean every individual component,
4. replace any damaged parts,
5. and reinstall the rebuilt carburetor.

11. Idle Air Control Valves Requires Adjustment

Idling on many bikes involves the use of the idle air control valves to control how much air your throttle plate allows past the throttle body, as the airflow alters the motorcycle’s idle speed.

If your bike’s idle air control valve falls out of adjustment or wears out from frequent use, your motorcycle’s engine will start sounding rough, particularly when running multiple electrical components and idling right after a cold start.

This is because your bike’s idle control valve is designed to sustain the engine’s idle speed against changes in the electrical current brought on by the battery strain of components, like radiator fans and LED lights.

Furthermore, your idle air control valve allows your idle speed to stay consistent during shifts in temperature and air quality despite the draw the cold weather adds to your battery.

Therefore, if your idle air control valve isn’t tuned correctly, your motorcycle engine will sound rough, especially when your battery is already under stress.