Carbureted Models Only
See Figures 1 and 2
On carbureted Toyotas with an engine modification system, a throttle positioner is included to reduce exhaust emissions during deceleration. The positioner prevents the throttle from closing completely. Vacuum is reduced under the throttle valve which, in turn, acts on the retard chamber of the distributor vacuum unit. This compensates for the loss of engine braking caused by the partially opened throttle.
For a description of the operation of the dual-diaphragm distributor, see Dual-Diaphragm Distributor.
Once the vehicle drops below a predetermined speed, the vacuum switching valve provides vacuum to the throttle positioner diaphragm; the throttle positioner retracts allowing the throttle valve to close completely. The distributor also is returned to normal operation.
- Start the engine and allow it to reach normal operating temperature.
- Adjust the idle speed.
Leave the tachometer connected after completing the idle a