Carbureted Engine

Fig. 39 Ignition timing control system.:

Fig. 40 Ignition timing control system.:

This system, Figs. 39 and 40, provides vacuum advance in response to manifold vacuum to optimize ignition timing during and after engine warm up. The distributor has two separate vacuum advance diaphragms. Diaphragm A operates on manifold vacuum. Diaphragm B also operates on manifold vacuum but has a thermovalve in the line. When engine coolant temperature is below the specified temperature of the thermovalve, the thermovalve is closed and vacuum is applied to diaphragm B to improve cold engine performance. When coolant temperature exceeds the calibration point of the thermovalve, the thermovalve opens and vacuum applied to diaphragm B is vented to atmosphere.