Carburettor

How carburettor works, its uses and the common issues.

Carburettor: This mechanical device blends air and fuel in a set ratio for the engine to run smoothly. The principle/phenomenon behind the operation of this device is the Vacuum Venturi Effect. Once the throttle is turned, it mechanically opens up a door way for air to pass through a venturi tube. As the air passes through, a proportional amount of fuel is brought in to the engine for combustion.

Carburettors were invented during a time when there were no significant improvements in the field of digital/electronic technology. As a result, a carburettor is a crude/mechanical way to tell what amount of fuel and air should go to the engine. However, by the 1980's inventors came up with a 'feedback carburettor' that could dynamically control the air and fuel mixture levels. The usage of sensors to pick up the amount of oxygen at the exhaust port gave the system a rough idea about the amount of air to be brought in. Then again, the feedback carburettor was considered to be highly complex and therefore difficult to maintain, as compared to the non-feedback mechanism and also the Fuel Injection mechanism.

A carburettor can make the bike smooth to ride, given that the carburettor has been properly tuned at par with the engine. However, as the motorcycles age, similar to how the parts of the bikes gets old, the carburettor ages too. Carburettors usually develop leaks in the system and as a result an unequal amount of air enters the engine and mixes with the fuel, leading to an inefficient combustion cycle. This leads to a number of problems including too much fuel brought in or the combustion chamber temperature being increased at a very high rate. Also, a carburettor is exposed to ambient conditions such as the weather, altitude, pressure and so on. On a cold day, for example, when the engine needs to start, fuel needs to be fed to the combustion chamber. However, the temperature outside condenses the fuel and takes time for it to be burnt. Vaporized fuel is ideal to get the engine up and running but with condensed fuel, the process takes longer and it might also need more fuel to be brought in to compensate. Therefore, ambient temperature is the chief factor that determines how fast an engine would start. Most bikes get the choke lever that sends in more fuel to get the engine idling properly and some bikes get the auto-choke feature which lets in fuel by itself. Altitude is also an issue since the pressure drops and the air becomes less dense. Less dense meaning a low number of oxygen molecules. This does not do good for the engine as it leads to something called the "over rich mixture". Pressure influences the fuel metering done by the carburettor, as the pressure varies, the float valve is confused and sends in more fuel.

Three main carburettor problems:

1. Rich Mixture: When too much fuel is pumped into the chamber, the mixture is rich. This occasionally results in poor fuel economy, black or sooty smoke from the exhaust and poor acceleration, all due to the inefficient combustion.

2. Lean Mixture: This time, too much air is brought to the combustion chamber and results in an uneven combustion cycle. This is the main reason why engines backfire. White/bluish smoke from the tail pipe and also bluing of the exhaust pipe is a common feature.

3. Improper Tuning: This cannot be termed as a problem as such but it depends on the know-how of the person using the bike or who checks the engine. Getting the air-fuel mixture screw is essential to get a proper and smooth running engine. Maintaining the engine is one main point when it comes to getting a smooth ride.

In the recent years however, there has been a significant decline in the number or vehicles, be it bikes or cars, fitted with a carburettor on the engine. The reasons could vary but a couple of the main reasons would be regarding the Emissions norms set by the country, almost all nations in the world adhere to cut down emissions by a considerably wide margin and carburetted engines is not worthy enough to fit into the list because of its imperfections while burning fuel. The other reason would be that the owner has to spend a lot of his time, money and brains just to get the mixture right - a bad idea for people running behind time- and manufacturers wouldn't lean on to the idea a product that does not sell in large volumes.

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