Small Engine Carburetion

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Small EngineCarburetion
Ch 8
Chapter Objectives - Upon completion of this
chapter you should be able to

• Explain theory of operation of a basic
  carburetor.
• I.D. and understand the function of all
  carburetor parts.
• Understand the effect of atmospheric pressure on
  the fuel system of a small gas engine.
• Differentiate between 3 basic types of fuel
  systems found on small gas engines.
• Perform adjustments on each carburetor type.
• I.D. properly service the 3 types of air intake
  systems.
• Understand the operation adjustment of an
  pneumatic and mechanical governor.

Revised 10/01
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Small EngineCarburetion
Ch 8

• Mix air fuel to a 151 ratio
• Vaporize fuel

Carburetor Functions
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Small EngineCarburetion
Ch 8
Elevation and its effect on Atmospheric Pressure
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Small EngineCarburetion
Ch 8
Determine proper Air Fuel Ratio under load by
sparkplug coloration
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Small EngineCarburetion
Ch 8
Venturi Principle
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Small EngineCarburetion
Ch 8
Carburetor Draft Types
Natural Draft (Horizontal)
Up Draft
Down Draft
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Small EngineCarburetion
Ch 8
Carburetion Fuel Systems
Suction Type BS (Vacu-jet)
Pump Type BS (Pulsa-jet)
Gravity Feed Type BS (Flo-jet)
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Small EngineCarburetion
Ch 8
Carburetor Components and Operation
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Small EngineCarburetion
Ch 8
Old style carburetor with an adjustable needle
valve
Newer style carburetor with a fixed Jet (Jet must
be replaced for altitude adjustment)
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Small EngineCarburetion
Ch 8
When performing an altitude adjustment the jet is
removed and replaced with a jet that has a
smaller orifice.
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Small EngineCarburetion
Ch 8
Diaphragm Type fuel pump
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Small EngineCarburetion
Ch 8
John Deere Small Engines Fuel Systems video
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Small EngineCarburetor
Ch 8
Pneumatic Governor
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Small EngineCarburetion
Ch 8
Mechanical Governor
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Small EngineCarburetion
Ch 8
Air Cleaner Servicing Oiled Foam
Wash with liquid detergent water
Wring out in a dry towel
Re-oil with motor oil
Squeeze out all excess oil
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Small EngineCarburetion
Ch 8
Air Cleaner Servicing Dry Element
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Small EngineCarburetion
Ch 8
Air Cleaner Servicing Dual Element