Fuel Injected motorcycles are fast taking over carbureted ones, which until the beginning of the new millennium ruled the roost. It wasn’t until 1980 that fuel injection made its way on a street going bike. As things stand today, almost every premium motorcycle comes equipped with an FI system. So while the good old grease monkeys still swear by the reliability, tune-ability and serviceability of carburetors, newer riders believe that fuel injection is better in every way. So how exactly are these two systems work? How exactly are they different and what are their respective virtues and vices? Let’s find out!
Carburetor is the most basic, and until recent times the most prevalent fuelling system used in two-wheelers, especially in India. To explain the basic working of a carburetor, think of it as a tube that feeds an air-fuel mixture into the cylinder from one end, with an air filter attached to another. Now, somewhere in the middle of this tube the air passage area is restricted to increase the velocity of the air passing through. This little area, or part of the carburetor system is known as venturi. By increasing the velocity of the air through the narrow area, a low pressure pocket is created, which in turn facilitates drawing fuel from a jet placed near the venturi through suction. This phenomenon is in line with Bernaulli’s principle which states that the velocity of a fluid (or air) passing through a tube is inversely proportional to the pressure created by it.
The amount of air sucked into the carburetor is decided by a valve at the end of the tube connected to the cylinder. This valve is termed as the throttle valve and is connected to the accelerator grip of your two-wheeler and controls the air-fuel flow through the throttle inputs provided by the rider. When you wring the throttle, the throttle valve opens – allowing a generous flow of air through the carburetor. Conversely, it’s closed when the throttle on the handlebar is fully rolled back.
The fuel jet, which is placed near the venturi draws its fuel directly from the fuel tank via a float chamber, which is a small reservoiur for fuel, with a float valve which cuts fuel supply when it’s full and resumes it when the jet is drawing fuel from it. The resultant air-fuel mixture is then supplied to the cylinder where combustion takes place.
This is a very basic explanation of how a carburetor works, though modern carburetors including constant velocity or CV carburetors are generally more complex in design. These carburetors make use of components like a diaphragm, needle valve and pilot jet to control the air-fuel mixture. The important point to note here, though, is that this entire setup is rather simple and is fully mechanical with no electronics or sensors coming into play.
Unlike carburetors, a Fuel Injection system is comprised of a complex set of electronics and sensors. In carbureted systems the fuel gets drawn from the tank, while in a Fuel Injected system it depends on a fuel pump installed inside the tank for a fine-grained control over fuel flow. The fuel injection nozzle also goes directly inside the combustion chamber. The pressurised fuel is very well atomised as a homogenous mist in case of FI systems, allowing for very efficient and clean combustion.
The fuel supply in case of FI is controlled through an electric brain, or ECU, which constantly makes complex calculations at a very high frequency to deliver the best air-fuel mixture possible. Based on a whole variety of parameters such as engine speed, throttle position, engine temperature and load etc the ECU directs the injectors to let in just the right amount of fuel with every intake stroke to facilitate the most efficient combustion.
Now, while the efficacy of an FI system has been proven to be superior to carburetor, it’s not that the two systems don’t have their distinct advantages and disadvantages. Here, we will discuss the merits and pitfalls of the two systems in brief bullet points.
Advantages of carburetors
- Carburetors cost less, are simple in operation and easy to repair or replace
- Carburetors allow the users to tune them to their requirements
- Since carburetors are not integrated into the engines, they can be serviced or replaced without touching the engine
Disadvantages of carburetors
- Not the most efficient systems, dated design
- Most carburetors have a slight lag, which results in relatively slow throttle response
- Certain components like diaphragm are relatively delicate and prone to damage
- Air fuel mixture fluctuates, affecting engine smoothness
Advantages of fuel injection
- Optimised air-fuel mixture and atomisation allows for cleaner, more efficient combustion
- Sharper throttle response
- Better fuel efficiency and marginally more power than carbureted systems
- They are typically maintenance free and does not break down
Disadvantages of fuel injection
- Substantially more expensive than carburetors
- Cannot be repaired with simple tools, have to be replaced, which is expensive.
- Cannot be customised, unless you go for custom ECU maps, which again is expensive
So while the advantages of an FI system are pretty clear despite its cost, you’d still be one among millions who still put their faith in the good old carb. Which tech do you prefer, and why? Do let us know your opinions through comments below.