Air/Fuel Mixture: Adjustments

Fig. 16 Equipment Hookup For Setting Idle Mixture Using Propane Enrichment Method:

Note: This procedure requires that the idle speed is properly set. Refer to IDLE SPEED before continuing with this procedure.

1. Start engine and run until cooling fan comes on.
2. Remove air cleaner intake tube from intake duct and connect tachometer.
3. Insert propane enrichment hose approx. 4 inches into air intake hose.
4. Note idle speed, slowly open propane valve.

Propane Enrichment RPM Curve:

5. Adjust propane to achieve the highest possible rpm gain over curb idle speed. Note RPM increase.

Expected result:
M/T 50 ± 20
A/T 30 ± 10

6. If rpm increase is correct, mixture is set correctly. If rpm increase was not correct proceed to the next step.

Note: If idle mixture plug has been previously removed go to step 17.

7. Stop engine.
8. Remove air cleaner.
9. Disconnect throttle cable.
10. Remove carburetor mounting nuts and the bolt securing the steel vacuum line manifold running behind carburetor.

Fig. 18 Gaining Access To The Mixture Adjustment Screw:

11. Lift carburetor clear of the mounting studs and tilt it backwards to remove bottom idle controller bracket retaining screw.

Fig. 19 Mixture Adjustment Screw Location:

12. Remove remaining idle controller screws and remove idle mixture screw cap.
13. Reattach idle controller bracket to carburetor.
14. Reinstall carburetor on intake manifold, using a new gasket.
15. Reattach throttle cable and check to ensure no vacuum lines were left off. Refer to THROTTLE CABLE for adjustment procedure.
16. Reinstall air cleaner.
17. Restart engine.
18. If enriched rpm was too low, air/fuel ratio is rich, turn the idle mixture screw 1/4 clockwise and retest. If enriched rpm was too high, air/fuel ratio is lean, turn the idle mixture screw 1/4 counterclockwise and retest.