O/T Distributor vacuum advance symptoms

55 50 Ron · Dec 10, 2012

What would a non-working distributor vacuum advance act like?

LJD · Dec 10, 2012

Timing doesn't change when you open up the carb and vacuum drops. It shows symptoms like a car does when the accelerator pump is bad in the carb. Stumbles when you revv it.

cole in mo. · Dec 10, 2012

A way to check it, pull the line off the manifold and suck on it. If you can hold a vacum its good, if you can suck through it, its bad.

MisterT · Dec 10, 2012

(quoted from post at 17:25:18 12/10/12) Timing doesn't change when you open up the carb and vacuum drops. It shows symptoms like a car does when the accelerator pump is bad in the carb. Stumbles when you revv it.

Also can cause over heating issues, but the biggest thing you will notice is a sudden decrease in miles per gallon.

Bob M · Dec 10, 2012

In addition to the symptoms the others note, a non-functioning vacuum advance can cause the engine to backfire out the exhaust when the throttle is suddenly closed from governed RPM.

Check by sticking on a timing light then noting the timing mark location with the engine idling. Now disconnect the vacuum advance hose and check it again. If the vacuum advance is working, the timing will mark will retard noticeably when the hose is disconnected.

Allan in NE · Dec 10, 2012

The ONLY symptom of a bad vacumn advance is poor(er) fuel mileage.

That is it's only purpose on this earth.

Allan

pete 23 · Dec 10, 2012

It also depends on where the vacuum line is hooked. Some are hooked directly to intake manifold, most are above the throttle shaft. The larger IH v8 gasoline engines hooked into intake manifold. You had to unhook them to time the engine with a light. With it unhooked and timed correctly the engine would labor, then you hooked it back up and it ran free. I remember a service station in town timed one with it hooked and that made timing about 14 degrees late. Was an easy fix to get the power back up for that customer . Other engines hooked that way also but this one always stuck in my mind.

Goose · Dec 10, 2012

I disagree. Had the vacuum advance fail on a Ford pickup once, and it ran fine, just sluggish and no get up and go.

Acted just like if the timing were set way slow, which in effect it was.

John B. · Dec 10, 2012

You'll notice when you start off from a stop that it don't want to go and it'll pop thru the carb until speed picks up and the mechanical advance kicks in! This is one symptom I experienced. There may be others.

Heat Houser · Dec 10, 2012

Alan, You are 100% correct. For those who disagree, consider Wide Open Throttle at full load. Vacuum is very low and the air/fuel mixture is fired at max mechanical advance. Vacuum advance is little to nonexistant

Watch the distributor on an old 1950's chevy six cylinder where the body was moved by the vacuum diaphram. When you go to WOT, the vacuum advance falls off. At partial throttle, vacuum advance is maxamized.

55 50 Ron · Dec 10, 2012

1950s Chevy 6 cylinder is exactly what I have and why I asked the original question.

O/T Distributor vacuum advance symptoms

55 50 Ron

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LJD

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cole in mo.

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MisterT

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Bob M

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Allan in NE

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pete 23

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Goose

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John B.

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Heat Houser

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55 50 Ron

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