How muc vacuum should I get?

[maytag]

ey all:
I posted this question in my other thread about burning up points, but what with the rest of the discussion, it sort of got buried. So I thought I'd just ask it again, This will allow others' searces to find it too, as I thin it's a valid and important question.

How much vacuum should I count on getting to pull a vacuum advance unit? My motor is a stock '76 1800.

I'd like to dal in the distributor and advance on the bench, before installation, but I can't measure the vacuum on mine riht now (see "Burning-up points" )

Has anyone measured it?

Idealy, I would like to make suer that when I apply that amount ofvacuum to the diaphragm, I get the full stroke on the rod, pulling in all of the available advance. This look slike it'll be tough to do once installed.

[majicwrench]

Maytag,
Not sure what you are setting up....my thoughts would be to stick with a basicly stock dist if a stock engine. But to your question..
A typical engine produces about 18" vacuum at idle on your typical gauge. Any basic engine, your family car etc, will pull the same vacuum as your stock fiat engine.

Sooo, how are you setting this up on a bench?? Do you have an old distributor machine??
Keith

[maytag]

Maytag,
Not sure what you are setting up....my thoughts would be to stick with a basicly stock dist if a stock engine. But to your question..
A typical engine produces about 18" vacuum at idle on your typical gauge. Any basic engine, your family car etc, will pull the same vacuum as your stock fiat engine.

Sooo, how are you setting this up on a bench?? Do you have an old distributor machine??
Keith

No, all I'm setting-up on the bench is the vacuum advance, nothing else. The reason I pulled it off and put the points type back in was because I could tell that the advance was not coming in. The rod was not moving. I know the diaphragm hlds vacuum, which is a good sign. SO all I'd like to do is make sure (prior to installation) that when the correct amount of vacuum is applied, the actuator rod will mve it's full stoke, bringing in all of the advance it was designed to do.

So to your 18".... did they really read it in inches? I can do that, for sure, but most of my automotive vacuum gauges are read in lbs, (aren't they? maye I'd better have another look at that.) And I know my mighty--vac that I'll be applying vacuum with reads in lbs, not inches.

[majicwrench]

Inches...good question!!! Gonna have to go look at my vac gauges too! Jeesh.
They all read the same units, whatever the units might be, unless you start using some really bizare gauges. Your mighty vac is a good tool,
Interesting that your diaphram holds vacuum yet won't move anything when vacuum applied. Let us know.
Keith, all 66" of me. I fit good in a Fiat!

[So Cal Mark]

your gauge is probably pressure/vacuum. Pressure is measured in lbs and vacuum in inches. Vacuum is calculated in inches of mercury; for instance it takes a specfic amount of vacuum to raise a measured amount of mercury one inch.

[maytag]

So I took a look, and sure enough; my guages measure "in/hg" (inches of mercury), not lbs. I think I was thrown-off because the gauge AlSO reads pressure, in lbs.


And here's the mity-vac gauge, also in/hg:

[maytag]

as it turns-out, the vacuum advance wasn't comin-in because the advance unit was installed incorrectly. The little white clip that threads-onto the end of the rod and then slips over the ball on the bottom of the pickup-plate was actually pushed-onto the ball all skewampus. (is that a word?)

It appears I'm getting about 12degrees of advance out of it now. I've reinstaleld it into the car and everything seems to be A-OK.