Why Do Motorcycles Have Multiple Carburetors?


Motorcycles change in design with your changing needs. If you need your machine to run on sports tracks, a higher power becomes necessary. Similarly, the vintage and heavier ones need more output too. In such cases, you often realize why do motorcycles have multiple carburetors.

While some motorcycles now have an injection system, the carburetors are still more famous. It is because of the simplification they bring to the 4-Stroke SI design at lower costs.

However, several issues come forward when working with multiple carburetors for drawing power. It needs you to understand the how’s and why’s we relate to the motorcycle working.

Here, I explain why do motorcycles have multiple carburetors and how they work with them. Moreover, I also establish the points to focus on while maintaining such motorcycle engines. A light review of the changes you will find with time helps to maintain steady performance.

Use of Carburetors in Motorcycles

The first idea you need to understand is that why motorcycles need carburetors for working. Every combustion engine uses the same principle of combining air and fuel for energy output. The intake of these two elements can either be separate or together for ignition.

Inside a spark-ignition engine of the traditional type, the mixture of fuel and air comes together. It ignites with the help of spark and gives expansion gases that deliver output power.

Hence, a suitable mechanism for giving this air-fuel mixture to the cylinder becomes necessary. Carburetors are the part that performs this action for your motorcycle in everyday life. 

Working Principle

Most carburetors will appear like a tube or a funnel when you look at them from the outside. However, their design is quite different from a simple pipeline to enable the air intake.

If you understand motorcycle acceleration, you know that the accelerator throttle does not control things directly. The throttle regulates the amount of air that goes into the cylinder instead of fuel.

Hence, when you give acceleration, the air quantity changes (I explain how later) going inside. This air passing through the carburetor goes through a venturi passage, where the pressure difference arises. Hence, the vacuum port of the venturi draws fuel to mix with this air and go ahead.

This mixture is the final one available for combustion in the engine. Hence, the higher the airflow, the better is the combustion and the higher the power you get. More intake pressure also creates more strokes, leading to higher RPM at the output of your engine. 

Carburetor Designs for Motorcycle Engines

To know why do motorcycles have multiple carburetors, their design understanding is critical. Now that you understand their function, motorcycles either work with single or different carburetors. It is dependent on the fact whether your motorbike has one or multiple cylinders.

While the lighter vehicles also use the same IC engine design, they usually have lower power needs. It means a single-cylinder fits fine for them. Motorcycles need space-friendly specs and also need a higher power. Hence, multiple cylinders are necessary for them more than the smaller drives. 

Single Carburetor Design

If your ride has a single-cylinder arrangement, the single carburetor design fits perfectly. The intake has the only unit and needs a single passage for the air-fuel mixture to reach in. Hence, this design is popular with 100 cc engines running around on the streets. 

Multiple Carburetor Design

The engines with more than one cylinders typically employ a multiple carburetor arrangement. These have a typical multiple piping inlet with each carburetor independent at the intake with others.

The relation between them only comes in at the tuning and final intake part. I will assist with the simple understanding of its necessity a bit later for the multiple carburetor efficiency. 

Why Multiple Carburetors?

So, after knowing the use of carburetors in motorcycles, you need to figure why there are multiple ones. In simple terms, the basic principle of air-fuel mixture intake is dependent on the quality aspect. It also includes the fact that a universal quantity needs to reach each cylinder engine.

If the cylinders are in line, a single carburetor starves to supply the sequence. It is because the suction vacuum of the first one interrupts the others. Hence, the firing order faces disturbance, with a power output not being smooth enough.

By using multiple carburetors, the passage for each intake is separate. It means a smooth and universal intake pattern for each suction stroke is available for each cylinder. Hence, this smoothens out the ripple we face in the power stroke graph for the engine output. 

Reasons For Use

Several reasons decide why do motorcycles have multiple carburetors for operation. Most of these orients around your requirements from the type of motorcycle you use. 

  • Motorcycles give you the same or even higher power than cars. However, the space restrictions do not big engine design. When using an in-line arrangement, the single carburetor has a constraint for the maximum inlet diameter for the pressure drop. 
  • For a single carburetor in multiple cylinders, fuel mixing also becomes difficult. Hence, sometimes the mixture can be too lean or thick. It disturbs the stoichiometric ratio that allows you a good combustion quality. 
  • By increasing the size of the carburetor, it also becomes difficult to position the engine. Hence, flexibility comes when you use multiple carburetor inlets instead of a single type. 
  • The power limitations do not trouble you with such an arrangement. It also helps to derive higher efficiency with the cylinder of lower diameter and more compact nature.

Acceleration Control Mechanism

As I include in the information before, your throttle does not control the fuel directly. Instead, it regulates the amount of air that goes through along with the fuel mixture. Hence, a mechanism needs to be in place to make sure this action is smooth. 

This mechanism uses a valve-like system to regulate the quantity of intake. However, the valve differs based on the connection style for operation.

Slide Type

Irrespective of single or multiple carburetors, the slide design fits perfectly fine. It has a simple slide connecting with the throttle control. Hence, the slide shifts as per the requirement to allow the airflow for combustion.

Butterfly Valve

This design is majorly famous as the one that provides you with constant velocity. Instead of using the simple slide design, it uses a butterfly valve for control purposes. The throttle change will position the valve to increase or decrease the flow of the combustible mixture. 

Issues With Multiple Carburetor Design

Like any other design, multiple carburetors have their own set of issues. The main factor that comes into play is the tuning of these carburetors for smooth power output. As I have in the earlier readings, the throttle controls the quantity of intake through the slide or butterfly arrangement.

Hence, if your acceleration is out of tune, the multiple carburetor design has ripples in output. It needs you to perform the tuning of the combustion side for making amends.

Other issues that surround when you use a motorcycle with multiple carburetors are:

  • Higher chances of fouling of the exhaust passage if the tuning is out of order. It creates cases of a blow past to happen in the line for silencer damages.
  • Any change in the orientation means you need to account for airflow. Hence, the inlet passages are all careful maintenance for good scavenging. 
  • Can lead to a situation where the design gets too bulky at the development stage. However, this does not concern you as a rider or a buyer as selling options are fool-proof. 

Multiple Carburetor Tuning

The adjustment of tuning includes the use of a specific tool that helps in the process. The entire idea of synchronization depends on the nature of vacuum build-up in the carburetor.

To judge this, the tube apparatus with a liquid level indicates the vacuum nature. Hence, you will get a fair idea of the scavenging nature and its efficiency. If the carburetor sync is out of tune, some units do not fire as well as they need to.

Each of these connects through linkages and springs that have tightening screws in between. With the help of these, you can adjust time timing and the opening limits too. 

Advantages of Multiple Carburetors

Several advantages come by understanding why do motorcycles have multiple carburetors. Most of these revolve around the fact that manufacturers prefer cost-efficient options.

  • You can give in-place repairs without too many part removals 
  • It does not need any automation to decide the timing or the quality of combustion. Hence, as a rider, your ability to make adjustments is also flexible. 
  • The quality of the material is not as decisive in the efficiency of working. It is because the simple nature of working does not have too high-pressure range.
  • Allows change of orientation or size in case you decide to make further modifications


With the power and size restrictions, it becomes clear that why do motorcycles have multiple carburetors. It also creates cleaner emissions as the correct stoichiometric ratio cancels out any afterburning.

Despite the rise of injection devices, carburetors still find wide usage. It gives a good idea to you for their credibility and simplicity in motorcycle working.

Hence, the overall power capacity from a compact design gives you a lean and sleek machine. It gives you the ideal power output for a strong drive for sports and adventure motorcycles!