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

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Presentation on theme: "1 Purpose of Carburetion A carburetors primary purpose is to produce a mixture of air and fuel for different engine operating conditions."— Presentation transcript:

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

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

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

4 4

5 5

6 6

7 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 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 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 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 11 Carburetion Atomization –Turning a liquid into little droplets Vaporization –Turning liquid droplets into a vapor or gaseous state

12 12 Carburetion Types of carburetors - air direction –Side draft

13 13 Carburetion Types of carburetors - air direction –Up Draft

14 14 Carburetion Types of carburetors - air direction –Down draft

15 15 Carburetor Circuits Float circuit –To maintain proper fuel level

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

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

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

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

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

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

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

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

24 24 Carburetor / Governor Air vane governor –Pneumatic –Flywheel air pressure

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

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

27 27 Carburetion Air Filters Foam type air cleaners (reusable)

28 28 Carburetion Air Filters Paper type air filters (replaceable)

29 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 30 Carburetor Adjustments Before making any adjustments clean and inspect parts for wear !!

31 31 Carburetor Exploded View

32 32 Running Conditions Too Rich –Air-fuel mixture with excessive fuel –HC and CO pollution –Exhaust black soot Too Lean –Air-fuel mixture lacking fuel –CO and NO X pollution –Engine overheating Just Right –Smooth engine operation –Rapid Acceleration –Low pollution / Clean Exhaust –Normal operating temperature

33 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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