How carbureted engine work?

During 90’s their was a common saying for vehicle’s starting trouble – carburetor mein kachra aa gaya hoga and this was quite true at times. In general, people assumed this to be true for both diesel as well as petrol vehicle but it wasn’t as only petrol engine require mixing of air-fuel before sending the charge to cylinder.
Carburetor was widely used in petrol engines until Multi-point fuel Injection (MPFI) came into market which simplified the process of preparing air fuel mix with increased fuel economy forcing carburetor to disappear from engine bay.
But still we have two wheeler market which rely on carburetor for achieving air-fuel mix as it helps to keep the bike cost at lower side compared to fuel injected bikes. Operation of carburetor is pure mechanical whereas fuel injected system is assisted via. electronic control unit to achieve better control over mix.
Lets understand in detail about carburetor operation –
Overview:
Carburetor is a mechanical device which mixes the air fuel in different amount based on various driving conditions. Depending upon accelerator position, carburetor adjust the ratio of air-fuel mixture before sending to engine cylinder.

Working:

Basic design of a carburetor¬†is a large vertical air pipe above the engine cylinders with a horizontal fuel pipe joined onto one side. As the air flows down the pipe, it has to pass through a narrow kink in the middle, which makes it speed up and causes its pressure to fall. This kinked section is called a ‘venturi’. The falling pressure of the air creates a sucking effect that draws fuel from the fuel pipe at the side.
Beneath the venturi, there’s a valve called the ‘throttle valve’. The more throttle open up, the more air flows through the carburetor and the more fuel it drags in from the pipe to the side. With more fuel and air flowing in, the engine releases more energy and makes more power and the vehicle goes faster. This throttle valve is connected through cable or mechanical linkage to vehicle’s accelerator.
The more accelerator we press, more air fuel will be sucked into carburetor and will be passed to engine.
Carburetor Cross Section (Image Source: Wikipedia)
At the top of carburetor, we have a valve known as ‘choke valve’, this valve is connected to the choke lever we find in few bike/car which helps to start the vehicle during winter season.
As soon as we pull the choke lever, this choke valve of carburetor closes-up the opening and blocks majority of the air flow to carburetor resulting in less air and more fuel suction to carburetor. This process will make air fuel mixture rich in fuel which in-turn help in igniting the mixture quick enough during cold weather and starting 4 stroke process.

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