A simple carburetor can only supply the correct air-fuel ratio at one throttle position. To address this, modern carburetors include additional systems like an idling system, auxiliary port system, power enrichment system, and accelerating pump system. These systems allow the carburetor to meet the engine's demands under different operating conditions like idling, cruising, acceleration, and high power.

1. CARBURETOR
Complete Carburetor

2. Drawback of Simple Carburetor
 A simple carburetor as described suffers from the fact that it
provides the required air-fuel ratio only at one throttle
position.
 At all other throttle positions, the mixture is either leaner or
richer depending on whether the throttle is opened less or
more.

3. Complete Carburetor
Complete Carburetor
 A simple carburetor is capable to supply a correct air-fuel
mixture to the engine only at a particular load and speed.
 In order to meet the engine demand at various operating
conditions, the following additional systems are added to
the simple carburetor.
 idling system
 auxiliary port system
 power enrichment by economizer system
 accelerating pump system
 choke

4. Idling System
Idling System

5. Idling System
Idling System Cont…
Cont…
 During starting or idling, engine runs without
load.
 The throttle valve remains in closed position.
 Engine produces power only to overcome friction
between the parts.
 A rich mixture is to be fed to the engine to
sustain combustion.

6. Auxiliary Port System
Auxiliary Port System

7. Auxiliary Port System
Auxiliary Port System Cont…
Cont…
• During normal power or cruising operation, the engine
runs for most of the period, the fuel economy has to be
maintained.
• Thus, it is necessary to have lower fuel consumption for
maximum economy.
• The opening of butterfly valve allows additional air to be
admitted.
• At the same time depression at the venturi throat gets
reduced, thereby decreasing the fuel flow rate.

8. Power Enrichment System
Power Enrichment System

9. Power Enrichment System
Power Enrichment System Cont…
Cont…
 To obtain maximum power, the carburetor must supply a
rich mixture.
 The additional fuel required is supplied by a power
enrichment system .
 A power enrichment system contains a meter rod
economizer
 This provides a larger orifice opening to the main jet as
the throttle is opened beyond a certain point.

10. Accelerating Pump System
Accelerating Pump System

11. Accelerating Pump System
Accelerating Pump System Cont…
Cont…
 During sudden acceleration of an engine (e.g.,
overtaking a vehicle), an extra amount of fuel is
vehicle)
momentarily required to supply a rich mixture.
 This is obtained by an accelerating pump system.
 It consists of a spring-loaded plunger, and the necessary
linkage mechanism.
 The rapid opening of the throttle moves the plunger into
the cylinder, and an additional amount of fuel is forced
into the venturi.

12. References
References