Adjusting Idle And Co

3. Detach air hose at diverter valve and insert a suitable plug.

Porsche 928 Twin Screw Intake
6. Connect CO level tester and separate tachometer according to instructions of manufacturer.



Engine in perfect mechanical condition. Ignition timing set correctly.

Adjustments must be made as quickly as possible, to prevent excessive heat in the intake ports.

1, Detach right air intake hose.

4. Install air cleaner upper section and air intake hose.

5. Run engine to operating temperature (80 to 90° C/ 176 to 194° F oil temperature). Use Special Tool 9122 or US 8025.

2. Remove air cleaner upper section.

3. Detach air hose at diverter valve and insert a suitable plug.

Porsche 928 Air Cleaner Straps


Make adjustments as quickly as possible to avoid excessive heat in intake ports and consequently wrong CO values.

Porsche 928 Twin Screw Intake

10. Remove special tool.

7. Adjust control screw on throttle housing until specified speed is reached.

b) Just turn control slightly, since the smallest adjustment will change CO level considerably.

9. Turn clockwise for richer or counterclockwise for leaner mixture.

10. Remove special tool.

Importa nt

It is essential to conform with the following points.

a) Always make CO level adjustments from lean to rich. Example: when mixture is too rich, first turn mixture control screw counterclockwise further than necessary and then clockwise to adjust to specifications.

Adjust mixture. Insert Special Tool 9134 through funnel-shaped opening into spring-loaded driver in mixture control unit. Press down special tool approx. 18 mm to engage spring-loaded drive in mixture control screw.

11. Accelerate engine briefly.

12. Wait until CO tester shows exhaust gas concentration at idle speed. See page 25-6 for adjusting data. If necessary, repeat adjusting procedures.

13. Recheck idle speed and correct, if necessary.

14. Remove plug after completion of adjustments. Attach air hose to diverter valve.

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