1. Carburetor Systems

2. The Float Bowl Fuel inlet system Stores fuel for immediate use
Maintains level
Viton Needle, brass seat
Dampening spring
Vapors vented to carbon canister

3. Idle Circuit Low airflow @ idle, main system will not operate
High vacuum under throttle plate draws fuel out idle ports
Sometimes adjustable
Idle air bleed helps atomize fuel

4. Transfer Circuit
Adds fuel as throttle plate opens, overcomes “lag”

5. Main Metering Circuit Fuel supplied by “main jets”
High venturi vacuum creates low pressure at nozzle tip
Atmospheric pressure in float bowl pushes fuel out discharge nozzle

6. Power Circuit Provides extra fuel at WOT
Mechanical power valve, maybe adjustable
Sometimes combination with metering rods
Flows through a circuit into main metering system

7. Accelerator Pump During sudden acceleration, mixture leans out
Pumps a lot of fuel into venturi

8. Choke Circuit Very rich A/F needed on cold starts
Closes off top of venturi to raise the vacuum level allowing greater fuel flow into manifold
Opens as engine warms up, or as an electric coil heats up

9. Choke Coil Operation

10. Choke Pulloff Forces the choke open slightly just after engine starts.
Position determined by
torque of coil
air velocity on blade
vacuum on piston
must adjust correctly!

11. Altitude Compensator
Compensates for altitude
Adjusts an air bleed

12. Idle Speed Control

13. Throttle Kicker Electric motor or solenoid, increases idle
1. Dashpot, 2. Throttle kicker, 3. Throttle cable, 4. Idle adjustment
Electric motor or solenoid, increases idle