Carburettors have served as a vital part of internal combustion engines (ICE) for many years, including motorcycles and vehicles with small engines. At heart, a carburettor is a device for mixing air and fuel in the proper proportions so the engine can burn the fuel efficiently. Fuel injection systems are common on newer motorcycles, however there are still motorcycles produced by manufacturers like Bajaj, KTM, and Triumph that still continue to use carburettors.
To define a carburettor, it is a mechanical device that blends air and fuel before sending it into the engine’s combustion chamber. The prime role of carburetors is to achieve an ideal air-fuel ratio for the vehicle to run properly. Once this ideal air or fuel ratio is achieved, we will have ideal combustion, optimal fuel usage, and improved engine performance.
In motorcycles carburettors additionally control the speed of the engine based on throttle input. When you twist your throttle you are asking the carburettor to let in more air-fuel mixture increasing speed and power output.
Despite the widespread shift towards fuel injection technology, carburettors continue to feature in some motorcycles. Brands like Bajaj and KTM still use carburettors in select models that are sold in cost-sensitive markets. Triumph, known for its retro-styled motorcycles, has also equipped some of its older and classic-styled bikes with carburettors to preserve that raw, mechanical riding experience.
The function of a carburettor is based on the Bernoulli principle, which states that airflow increases, and as a result, pressure drops, allowing fuel to be drawn into the stream. Here's how it operates:
Air enters the carburettor through the air filter.
As air passes through a narrowed venturi (a constricted section), its speed increases, and pressure drops.
This pressure drop draws fuel from the float chamber into the air stream.
The air and fuel mix is then delivered to the engine’s combustion chamber for ignition.
Choke: Temporarily restricts airflow to enrich the fuel mixture during cold starts.
Throttle Valve: Regulates how much of the mixture enters the engine, directly influencing speed and power.
Jet Needles: Meter and spray fuel into the air stream for atomisation.
Float Chamber: Maintains a steady level of fuel for consistent performance.
Main Nozzle and Fuel Jets: These determine the amount of fuel delivered depending on engine load and throttle position.
This fundamental mechanical operation is why a carburettor works so effectively in multiple driving conditions, especially when electronics are not desired or required.
In the case of a carburettor, one of its main functions is to deliver an air-fuel mixture in the correct ratio, which for petrol engines is usually 14.7:1. Whether the driver was on cruise control or performing hard acceleration, the carburettor adjusted the mixture made available to the engine.
The carburettor is directly connected to the throttle. The throttle valve opens wider as the rider twists the throttle grip, allowing more air-fuel mixture into the engine. This leads to a higher combustion impact, resulting in an increase in RPMs and speed.
Effective fuel combustion depends on the fuel being atomised as well as possible, and the carburettor supplies petrol sufficiently vaporised so that it is well burned in the engine, thus allowing for better ignition and lower unburnt emissions.
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Simple Design: Fewer components mean lower chances of failure.
Ease of Maintenance: Can be cleaned and serviced with basic tools.
Cost-Effective: Ideal for budget motorcycles and older models.
Tuning Friendly: Riders can manually adjust the air-fuel mix for performance tuning.
These factors make carburettors a go-to choice for certain Bajaj, KTM, and Triumph motorcycles, especially in markets where simplicity and affordability are priorities.
Less Efficient: Compared to fuel injection, carburettors are not as precise.
Environmental Sensitivity: Performance may vary with changes in altitude or temperature.
Inconsistent Mixture: Manual tuning may result in inefficient combustion and higher emissions.
Fuel injection systems employ a variety of sensors and electronic controls to regulate air-fuel mixtures with extremely high precision. They respond quickly to riding conditions, are more fuel-efficient, and produce lower emissions.
Carburettors are mechanical, they will not auto-adjust. Carburettors may not be high-tech, but the simplicity attracts riders wanting something mechanical that will take little maintenance and can be physically tuned.
Despite their drawbacks, carburettors are far from obsolete. Motorcycles like the Bajaj Pulsar 150, KTM 200 Duke (earlier versions), and some Triumph Bonneville variants continue to use them in specific models. Riders appreciate the ease of repair and the raw riding feel they provide.
If you're wondering which carburettor is used in which engine, the answer is typically single-cylinder or twin-cylinder petrol engines in motorcycles and small vehicles.
Clean the Jets: Dirt or deposits can clog fuel flow, affecting performance.
Replace Air Filters: A clogged filter can disrupt the air-fuel mix.
Check Float Chamber: Ensure it’s free of debris and allows proper fuel flow.
Inspect Fuel Lines: Any blockages or cracks can impact carburettor efficiency.
Delayed acceleration
Engine stalling
Hard starting
Unstable idling
Timely servicing by a trained technician can prevent these issues and ensure consistent performance, especially in carburettor-equipped motorcycles.
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As technology advances from carburettor systems to fuel-injected systems, many motorcycles still use the carburettor function. For some riders, it may be for cost-saving reasons, maintenance reasons, or just a passion for mechanical simplicity. Regardless, carburettors are still used in a very large segment of riders.
So, if you ride an older Bajaj, KTM, or Triumph, or you tend to choose budget-friendly motorcycles, then how the carburettor works and overall maintenance can make your ride a more enjoyable experience. On the other hand, if you are a rider who pushes for performance or rides in diverse conditions, fuel injection may perform in a more efficient manner and offer performance advantages.
Ultimately, your choice should depend on your bike's usage, riding style, and willingness to manage maintenance—because both systems offer unique advantages in the world of motorcycles.
