RPM drops with Vacuum Gauge hooked up?

This topic has 1 reply, 2 voices, and was last updated 11 years, 7 months ago by R.G.Young,Jr.

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April 17, 2013 at 4:27 am #515880
SDMAN1981
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OK today I hooked up a Vacuum Gauge and the engine’s RPM dropped 200-300 RPM then when I hooked the distributor vacuum advance back up it went back up to normal RPM 950. Is that normal?
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April 17, 2013 at 12:16 pm #515932
R.G.Young,Jr
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that is normal if you had disconnected the vacuum advance to hook up the vacuum gage. a vacuum gauge should be connected straight to the intake manifold or through a fitting that does not control a function of the engine at the time of testing i/e modulator valve, brake booster, vacuum reservoir tank etc, if you were working on a vehicle that has one, if not, you can tee into an existing manifold vacuum source to obtain the readings you need.
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