Post on 24-Dec-2015
Carburetor Systems
The Float Bowl• Fuel inlet system• Stores fuel for
immediate use• Maintains level
• Viton Needle, brass seat
• Dampening spring• Vapors vented to
carbon canister
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
Transfer Circuit
• Adds fuel as throttle plate opens, overcomes “lag”
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
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
Accelerator Pump
• During sudden acceleration, mixture leans out
• Pumps a lot of fuel into venturi
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
Choke Coil Operation
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!
Altitude Compensator
• Compensates for altitude• Adjusts an air bleed
Idle Speed Control
Throttle Kicker
• Electric motor or solenoid, increases idle
1. Dashpot, 2. Throttle kicker, 3. Throttle cable, 4. Idle adjustment