Bert---The vacuum interruption to the ignition retard is meant to take
place when the coolant gets hot, as when idling in traffic. This vacuum
supply is only present when the throttle is closed, as the port for this
vacuum is between the throttle plate and the intake manifold. (When the
throttle is opened, this source of vacuum disappears, and no vacuum is
present to retard the ignition timing.) If you are finding that your
idle rpms increase while no coolant temperature changes are taking
place, the culprit here may be the carburetor bi-pass valve(s). To be
certain, temporarily block off the vacuum line that goes to your
ignition retard pot. If the idle continues to increase in the situations
you described, it obviously is not because of this temperature
compensator in the radiator water hose.
Check the Bentley Manual on how to set the bi-pass valve, if necessary.
Dick T.
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