This section contains only tune-up adjustment procedures for carburetors. Descriptions, adjustments, and overhaul procedures for carburetors can be found in the Fuel System section.
When the engine in your Subaru is running, the air-fuel mixture from the carburetor is being drawn into the engine by a partial vacuum which is created by the movement of the pistons downward on the intake stroke. The amount of air-fuel mixture that enters into the engine is controlled by the throttle plates in the bottom of the carburetor. The throttle plates are connected by the throttle linkage to the accelerator pedal in the passenger compartment of the Subaru. When you depress the pedal, you open the throttle plates in the carburetor to admit more air-fuel mixture to the engine.
When the engine is idling, it is necessary to have the throttle plates open slightly. To prevent having to hold your foot on the pedal when the engine is idling, an idle speed adjusting screw is added to the carburetor linkage.
The idle adjusting screw contacts a lever (throttle lever) on the outside of the carburetor. When the screw is turned, it either opens or closes the throttle plates of the carburetor, raising or lowering the idle speed of the engine. This screw is called the curb idle adjusting screw.
A special mixture circuit is incorporated into the carburetor to enable the engine to run smoothly at idle. This circuit is controlled by the mixture screw, which determines the amount of fuel admitted at idle.
| Fig. 1: Plug secondary air cleaner hose and/or purge
hose
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| Fig. 2: Location of carburetor adjusting screws
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