Carburetor - Subaru EX13 Service Manual

12. CARBURETOR

12-1 SPECIFICATIONS
A/C Type
Main Jet
Pilot Jet
Pilot Screw Turning
12-2 FUNCTIONS AND CONSTRUCTION
12-2-1 FLOAT SYSTEM
The float chamber is located below the carburetor body. Through the operation of the float and the needle
valve, the float chamber maintains a constant fuel level while the engine is working.
The fuel flows from the tank into the float chamber through the needle valve. When the fuel rises to a
specific level, the float rises. When the buoyancy of the float is balanced with the fuel pressure, the needle
valve shuts off the fuel passage, thereby maintaining the fuel at the predetermined level.
12-2-2 PILOT SYSTEM
The pilot system supplies fuel to the engine during idling and low-speed operation.
Fuel is initially metered by the main jet and then metered once again by the pilot jet. At the pilot jet, the fuel
is mixed with air metered by the pilot air jet and then the fuel/air mixture is fed to the engine through the pilot
outlet and the bypass. During idling, fuel is fed to the engine mainly through the pilot outlet.
12-2-3 MAIN SYSTEM
The main system feeds fuel to the engine at medium and high speed operation.
Fuel is metered by the main jet and flows into the main nozzle. Air metered by the main air jet is mixed with
fuel through the bleed holes of the main nozzle. The fuel/air mist is injected into the Venturi and mixed once
again with air from the air cleaner. This fuel/air mixture is now of optimum concentration and is fed into the
combustion chamber of the engine.
12-2-4 CHOKE SYSTEM
The choke system is for easier start of the engine in cold weather conditions.
When the engine is started with a closed choke, the negative pressure applied to the main nozzle increases.
This causes a larger amount of fuel to be drawn into the carburetor, which in turn makes it easier to start
the engine.
EX13 EX17
STD DUAL STD
70.0 68.8 81.3
40.0 40.0 40.0
1-3/4 ← 1-1/4
- 57 -
EX21
DUAL STD DUAL
80.3 86.3 83.8
40.0 41.3 ←
← 1 ←
EX27
STD DUAL
98.0 96.0
40.0 ←
1-1/2 ←