CARBURETOR CIRCUITS
AND COMPONENTS
CBC AUTOMOTIVE
TECHNOLOGY
BASIC CARB DESIGN
• Conventional Design
• Computer Control for Better Fuel
Metering
• 1,2,3,4 barrel carbs
Pg 7
CARBURETOR SYSTEMS
• FLOAT SYSTEMS
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Float Material
Maintains Level
Float setting
Viton Needle and Seat
Dampening Spring
Float Bowl
Construction
– Float Drop
FLOAT BOWL VENT
• Vented to outside
atmosphere
• Vapor Seperator
• Mechanical Vent
• Dirty air filters affect
pressure in bowl
• Usually located near
center of bowl
Pg 8
IDLE SYSTEM
• Not enough airflow
at idle to allow main
system to operate
• Manifold vacuum is
high to draw fuel out
idle ports
• Usually adjustable
• Idle air bleed helps
atomize fuel and
prevents siphoning
Pg 8
TRANSFER CIRCUIT
• Transfers fuel off in
Off idle mode
• Adds fuel to mixture
as throttle plate
opens to cover “sag”
MAIN SYSTEM
• Fuel supplied by
“main jets”
• Operates under
high venturi
vacuum
• Atmospheric
Pressure pushes
fuel out discharge
nozzel
ACCELERATOR PUMP
SYSTEM
HOT IDLE COMPENSATOR
• Allows mixture to be lean out during hot idle
conditions caused by excessive fuel vapor
CHOKE TYPES
• Automatic Chokes
– Manual Hot Air
– Electric
• Integeral Choke
• Divorced Choke
Pg 10
CHOKE SYSTEM
• Operates when cold
and low rpm
• Sometimes fuel
extracted from air
bleed holes
• Allows 5:1 mixture
• Vacuum Break or
Choke Pull Off
CHOKE SYSTEM
CHOKE COIL OPERATION
CHOKE PULLOFF
• Forces the choke
open slightly just
after engine starts.
• Position determined
by
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torque of coil
air velocity on blade
vacuum on piston
must adjust correctly!
POWER CIRCUITS
• Mechanical Power
Valve
• Adjustable
• Sometimes
combination with
metering rods
• Flows through a
circuit into main
metering system
Pg 8
VACUUM POWER VALVE
• Different locations on
carbs. Usually in
bowl area.
• Supplies Extra fuel
under heavy loads
• Operated by
Manifold Vacuum
BAROMETRIC PRESSURE
COMPENSATOR
• Compensates for
altitude
• Fairly troublefree
THROTTLE POSITION
SENSOR
IDLE SPEED CONTROL
A/C IDLE SOLENOID
• Used with A/C
• Compensates for
drag on engine
caused by
Compressor
• Adjustment is
usually seperate from
Curb Idle rpm.
TYPES OF CARBURETORS
TERMINOLOGY
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Emulsion
Float Circuit
Lean
Metering
Metering Rod
Power Valve
Rich
Stoichiometric ratio
• Throttle Kicker
• Throttle stop
solenoid
• Transfer slot
• Vaporization
• variable venturi
• Venturi
• Air Bleed