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Purpose of Carburetion

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Presentation on theme: "Purpose of Carburetion"— Presentation transcript:

1 Purpose of Carburetion
A carburetor’s primary purpose is to produce a mixture of air and fuel for different engine operating conditions.

2 Purpose of Carburetion
Store Deliver Filter Mix air and fuel Meter air and fuel

3 Idle Mixture screw Idle Speed Screw Throttle Plate Choke Plate Float Pilot Jet Float Bowl Main Jet Pedestal




7 Carburetion Air-fuel Requirements
Ratio of air to fuel. Stoichiometric ratio of 14.7:1 Example 14.7 lbs of air to 1 lb of fuel Fuel ratios Rich / lean

8 Carburetor Operating Conditions
Cold Choke / prime Low speed Idle Mid speed Idle and high speed Acceleration Accelerator pump High speed Main discharge nozzle

9 Carburetion Pressure Differences
Vacuum Pressure less than atmospheric pressure Atmospheric pressure Force of air on a surface at 14.7:1psi Venturi principle A restriction in an air passage which causes an increase in air speed and a decrease in air pressure

10 Carburetion Pressure Differences
Air horn Air enters at Atmospheric pressure Venturi High vacuum is created Engine side Low vacuum created on the intake stroke

11 Carburetion Atomization Vaporization
Turning a liquid into little droplets Vaporization Turning liquid droplets into a vapor or gaseous state

12 Carburetion Types of carburetors - air direction Side draft

13 Carburetion Types of carburetors - air direction Up Draft

14 Carburetion Types of carburetors - air direction Down draft

15 Carburetor Circuits Float circuit To maintain proper fuel level

16 Carburetor Circuits Choke circuit
Provides a rich air-fuel mixture for cold starts

17 Carburetor Circuits Throttle
Regulates air –fuel mixture entering the cylinders

18 Carburetor Circuits Idle circuit
Supplies air-fuel mixture when the throttle is closed for low speed operation

19 Carburetor Circuits High Speed circuit Full throttle
Maximum air – fuel flow to develop full speed and power

20 Carburetor Circuits Accelerator circuit
Provides additional fuel to maintain the air fuel ratio when the throttle is quickly opened.

21 Carburetor Circuits Primer circuit
Forces addition fuel into the engine prier to cold starting

22 Carburetor Circuits Diaphragm uses atmospheric pressure and vacuum to move fuel into a chamber of the carburetor to be used as needed

23 Carburetion / Governors
Manual throttle controls Governor throttle controls Limit low speed Limit high speed Maintain constant speed

24 Carburetor / Governor Air vane governor Pneumatic
Flywheel air pressure

25 Carburetion / Governors
Centrifugal (mechanical) governor Rotating mechanical force

26 Carburetion Air Filters
Air cleaner purpose (3) Filter air to remove dirt Protect against back fire Quiet engine operation

27 Carburetion Air Filters
Foam type air cleaners (reusable)

28 Carburetion Air Filters
Paper type air filters (replaceable)

29 Carburetor Adjustments
Before making any adjustments clean and inspect parts for wear !! Rough adjustment Fine adjustment Idle mixture adjustment High speed mixture adjustment Rpm adjustment

30 Carburetor Adjustments
Before making any adjustments clean and inspect parts for wear !!

31 Carburetor Exploded View

32 Running Conditions Too Rich Too Lean Just Right
Air-fuel mixture with excessive fuel HC and CO pollution Exhaust black soot Too Lean Air-fuel mixture lacking fuel CO and NOX pollution Engine overheating Just Right Smooth engine operation Rapid Acceleration Low pollution / Clean Exhaust Normal operating temperature

33 Carburetion The purpose of the fuel system is store, deliver, mix and meter air and fuel for the engine to function over a variety of operating conditions.

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