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Functions of Carburetors

. Functions of Carburetors. A Mixing ValveMixes Fuel

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Functions of Carburetors

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    2. Functions of Carburetors A Mixing Valve Mixes Fuel & Air Meters Fuel Flow Atomizes Fuel for Use Controls Air Flow Engine Speed

    3. Ways to Classify Carburetors Size: (2) Air Flow Direction: (3) Fuel Type: (4) Barrels: (3) General: (3)

    6. Carburetor Parts & Their Functions In order to understand how each part of a carburetor works you should first build one. Building a carburetor on paper will allow you to see how each part works and why it is needed.

    7. Step #1: Air Horn Simple Round Metal Tube Flange Bolts to Intake Manifold Serves as an Air Passage for Air Entering the Engine

    8. Step #2: Fuel Bowl Attached to Air Horn Holds a Supply of Gas Float Inside Bowl: (3) Vent: (2)

    9. Step #3: Main Discharge Tube Allows Fuel to be Transfered from the Fuel Bowl to the Air Horn.

    10. Step #4: The Venturi A vacuum is needed to transport the fuel. The engine doesn’t create enough vacuum by itself. The Venturi increases air speed: (4)

    12. Step #5: Secondary Venturi Creates more vacuum. Position: (2) Multiples the vacuum. “Booster Venturi” Some carburetors have a 3rd venturi.

    13. Step #6: Air Bleed Reduces droplet size Introduces a stream of air into the fuel traveling up the main discharge tube. Smaller droplets carry into the engine properly.

    14. Step #7: Jets Introduction: (1) Purpose & Operation: (4)

    15. Step #8: Choke Valve Purpose: (2) Placement: (1) Operation: (2)

    16. Step #9: Throttle Valve The Engine Will Now Start! How will it Run? Throttle Butterfly Controls the Engine’s Speed: (3)

    18. Circuits The carburetor is complete but it still far from perfect! What are Circuits? Types of Circuits: (7) Purpose of Circuits: (1)

    19. Engine Problems Kept on Track By Circuits: Idle: Partial Throttle Operation: High Speed Cruising: High Speed Full Power: Acceleration Hesitation: Rich Mixture for Cold Starting:

    20. Small Engine Carburetors Types: Float Type Suction Type Pulsating Suction Lift Type Diaphram Type

    21. Float Type Carburetor Now Common on Briggs & Stratton Engines Fuel Bowl & Float System: (6)

    22. Suction Type Carburetor: (Vacu-Jet) Common in older Briggs & Stratton engines. Suction tubes pull the fuel up.

    23. Pulsating Suction Lift Carburetor: (Pulsa-Jet) Briggs & Stratton Pulsa-Jet Has a fuel pump built in: (1) Provides more Hp than a suction type: (2) Allows the air tube in the carb. to be larger b/c the fuel does not have to be lifted so far.

    25. Diaphram Carburetor Has flexible diaphrams: (1) Allows function at any position Popular on 2-cycle engines

    27. Despite all of it’s advances the carburetor is still a compromise of efficiency. The carburetor’s limitations have pushed the industry towards fuel injection.

    28. Fuel Injection Arrangements Direct Fuel Injection: Throttle Body Fuel Injection: Multi-Point (Port) Fuel Injection:

    29. Direct Fuel Injection Fuel injected directly into the combustion chamber. Fuel injector nozzle is also located in the combustion chamber. Very common in diesel engines.

    30. Throttle Body Fuel Injection Injectors are located in the throttle body. Throttle body is the intake cavity or intake manifold. The Carburetor is removed from the intake manifold and simply replaced by a fuel injection system. Disadvantage: (1)

    31. Multi-Port (Point) Fuel Injection Uses one injector located: At the mouth of the intake valve -or- At the mouth of an individual intake port that is connected to only one intake valve. Much more efficient Chrysler began this in the late 70’s, Ford mid 80’s, Chevy Vortex

    33. Methods of Fuel Injection Mechanical: (2) Electronic Fuel Injection: (4) Advantages: (9)

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