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5.6
Section 5
Fuel System and Governor
Figure 5-4. Main Circuit.
Check Valve Spring
Outlet Check Valve
Leak Jet
Adjustment Screw
Diaphragm Spring
Pump Diaphragm
Inlet Check Valve
ACCELERATOR PUMP
ASSEMBLY
(Some Carburetors)
Fuel Shut-Off Solenoid
with Main Jet
Main Jet
Main Nozzle
Throttle Valve
Choke Valve
Main Air Bleed Jet
Accelerator Pump Nozzle
Bowl Vent
Fuel Inlet
Float Valve Seat
Float Valve
Main Jet
Float
Main Emulsion
Hole
Idle Speed
(RPM)
Adjustment
Screw
Air
Fuel
Mixture
Main Circuit: (See Figure 5-4) At high speeds/loads the engine operates on the main circuit. As a metered
amount of air is drawn through the main air bleed jet, fuel is drawn through the main jet. The air and fuel are
mixed in the main nozzle and then enter the main body of airflow, where further mixing of the fuel and air takes
place. This mixture is then delivered to the combustion chamber. The carburetor has a fixed main circuit; no
adjustment is possible.