Fuel demand is low at idle and there is more than enough manifold vacuum to draw sufficient fuel for combustion, even if the fuel pump is switched off.
22.
This had the drawback that manifold vacuum varies depending on throttle position, and is almost non-existent under wide-open throttle, when the wipers would slow down or even stop.
23.
The ASV has three openings : one is connected to the manifold vacuum, another is connected to the exhaust pipe and the third is open to the atmosphere.
24.
Loss of manifold vacuum when the engine was working hard, or at wide open throttle, necessitated using a vacuum booster pump which was usually part of the fuel pump.
25.
On some vehicles, a temperature sensing switch will apply manifold vacuum to the vacuum advance system when the engine is hot or cold, and ported vacuum at normal operating temperature.
26.
This instrumentation usually included a vacuum gauge to indicate intake manifold vacuum, a special odometer to measure distance traveled to hundredths of a mile, and a burette to measure gasoline usage.
27.
It is designed to open the purge vent line, between the canister and the engine, to enable manifold vacuum to pull air through the canister and purge it of fuel vapors.
28.
This allows more accurate control of ignition timing, as well as the ability to alter timing based on factors other than engine speed and manifold vacuum ( such as engine temperature ).
29.
All the gauges are Dakota Digital and include : speedometer, tachometer, head temperature, vacuum, fuel pressure, volt meter, fuel level, oil pressure, and oil temperature, intake manifold vacuum, and air / fuel mixture.
30.
Setting the correct spark distributors rely on inertia ( by using rotating weights and springs ) and manifold vacuum in order to set the ignition timing throughout the engine's RPM and load range.
