Toyota Corolla 1970-1987 Repair Guide

Carburetor Auxiliary Slow System


A carburetor auxiliary slow system is used on 1970-71 3K-C engines. It provides uniform combination during deceleration. The components of the auxiliary slow system consist of a vacuum operated valve, a fresh air intake, and a fuel line which is connected to the carburetor float chamber.

During deceleration, manifold vacuum acts on the valve which opens it, causing additional air/fuel mixture to flow into the intake manifold. The additional mixture aids in more complete combustion.


  1. Remove the hoses from the auxiliary slow system unit.
  3. Unfasten the recessed screws and withdraw the system as a complete unit. Installation is performed in the reverse order.


See Figure 1

  1. Start the engine, allow it to reach normal operating temperature, and run it at normal idle speed.
  3. Remove the rubber cap from the diaphragm assembly and place your finger over the opening. There should be no suction at idle speed. If there is, the diaphragm is defective and the unit must be replaced.
  5. Pinch the air intake hose which runs from the air cleaner to the auxiliary slow system. There should be no change in engine idle with the hose pinched.
  7. Disconnect the air intake hose at the auxiliary slow system. Race the engine. Place your finger over the air intake. Release the throttle; suction should be felt at the air intake.
  9. If any of the tests indicate a defective auxiliary slow system, replace it as a unit.

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Fig. Fig. 1: Inspecting the auxiliary slow system diaphragm