Purpose of Carburetion A carburetor’s primary purpose is to produce a mixture of air and fuel for different engine operating conditions.

Purpose of Carburetion Store Deliver Filter Mix air and fuel Meter air and fuel

Carburetion Air-fuel Requirements Ratio of air to fuel. Stoichiometric ratio of 14.7:1 Example 14.7 lbs of air to 1 lb of fuel Fuel ratios Rich / lean

Carburetor Operating Conditions Cold Choke / prime Low speed Idle Mid speed Idle and high speed Acceleration Accelerator pump High speed Main discharge nozzle

Carburetion Pressure Differences Vacuum Pressure less than atmospheric pressure Atmospheric pressure Force of air on a surface at 14.7:1psi Venturi principle A restriction in an air passage which causes an increase in air speed and a decrease in air pressure

Carburetion Pressure Differences Air horn Air enters at Atmospheric pressure Venturi High vacuum is created Engine side Low vacuum created on the intake stroke

Carburetion Atomization Vaporization Turning a liquid into little droplets Vaporization Turning liquid droplets into a vapor or gaseous state

Carburetion Types of carburetors - air direction Side draft

Carburetion Types of carburetors - air direction Up Draft

Carburetion Types of carburetors - air direction Down draft

Carburetor Circuits Float circuit To maintain proper fuel level

Carburetor Circuits Choke circuit Provides a rich air-fuel mixture for cold starts

Carburetor Circuits Throttle Regulates air –fuel mixture entering the cylinders

Carburetor Circuits Idle circuit Supplies air-fuel mixture when the throttle is closed for low speed operation

Carburetor Circuits High Speed circuit Full throttle Maximum air – fuel flow to develop full speed and power

Carburetor Circuits Accelerator circuit Provides additional fuel to maintain the air fuel ratio when the throttle is quickly opened.

Carburetor Circuits Primer circuit Forces addition fuel into the engine prier to cold starting

Carburetor Circuits Diaphragm uses atmospheric pressure and vacuum to move fuel into a chamber of the carburetor to be used as needed

Carburetion / Governors Manual throttle controls Governor throttle controls Limit low speed Limit high speed Maintain constant speed

Carburetor / Governor Air vane governor Pneumatic Flywheel air pressure

Carburetion / Governors Centrifugal (mechanical) governor Rotating mechanical force

Carburetion Air Filters Air cleaner purpose (3) Filter air to remove dirt Protect against back fire Quiet engine operation

Carburetion Air Filters Foam type air cleaners (reusable)

Carburetion Air Filters Paper type air filters (replaceable)

Carburetor Adjustments Before making any adjustments clean and inspect parts for wear !! Rough adjustment Fine adjustment Idle mixture adjustment High speed mixture adjustment Rpm adjustment

Carburetor Adjustments Before making any adjustments clean and inspect parts for wear !!

Carburetor Exploded View

Running Conditions Too Rich Too Lean Just Right Air-fuel mixture with excessive fuel HC and CO pollution Exhaust black soot Too Lean Air-fuel mixture lacking fuel CO and NOX pollution Engine overheating Just Right Smooth engine operation Rapid Acceleration Low pollution / Clean Exhaust Normal operating temperature

Carburetion HAVE A NICE DAY The purpose of the fuel system is store, deliver, mix and meter air and fuel for the engine to function over a variety of operating conditions. HAVE A NICE DAY