Throttle Plate Adjustment

Fig. 114 Throttle Body:

The throttle body, Fig. 114, is a single-barrel side-draft type. The lower portion of the throttle valve is heated by engine coolant from the cylinder head. The idle adjustment screw which varies the amount of air bypassing the throttle plate and the charcoal canister purge/vent port are located on the top of the throttle body. A dashpot is used to slow the rate at which the throttle valve closes.

Fig. 113 Throttle Stop Adjustment:

CAUTION: Do not adjust the throttle stop screw
The throttle plate stop screw, Fig. 113, is not used to adjust the idle, it is primarily used to keep the throttle plate from binding in its bore. The position of the throttle at idle is critical in producing the correct vacuum values at the various vacuum ports, and is adjusted at the factory.

Fig. 112 Checking Idle Vacuum At The Throttle Housing:

1. With the engine at its normal operating temperature (cooling fan should cycle ON and OFF at least once), disconnect from the throttle body, the hose that connects to the charcoal canister. Connect a vacuum gauge to the throttle body, Fig. 112.
2. Vacuum availability should be:
With the engine at idle, no vacuum should be available.
With the throttle opened just off idle, vacuum should be available.
NOTE: If no vacuum is available when the throttle valve is opened, check the throttle body for a clogged vacuum port, and clean with carburetor cleaner.
3. Switch the engine OFF, and check the throttle cable for smooth operation.
4. If the throttle valve assembly fails any of the above tests, check for:
a. Excessive wear or play in the throttle valve shaft.
b. Sticky or binding throttle lever at the fully closed position.
c. Clearance between the throttle stop screw and the throttle lever at the fully closed position.
5. If there is excessive play in the throttle shaft, or if the shaft is sticking, replace the throttle body.