Vacuum Test

[spinelll]

I recently performed a vacuum test on my '30 roadster. It can be seen here:
https://www.youtube.com/watch?v=dcHq-n6JHIQ

The 1st reading (00:05) is at full retard.
The 2nd reading (00:50) is 3/4 towards advanced.
The 3rd reading (01:10) is full advanced.

Two questions:
1. Are these "normal" readings?
2. There are small spikes at around 1:16, 1:18, 1:20 and others. Does that indicate a slightly sticky valve?

Thanks
Leo

[tbirdtbird]

the engine struggles to run at full retard so I would ignore 1st reading.

readings 2 and 3 seem acceptable; not sure you will ever have a perfectly steady vacuum reading on a 4-cyl motor. Valve guides could be worn a bit, too

For kicks, we assume you are putting MMO in the tank (4 oz per 10 gallons)? Todays crapahol is so darned dry the valves get almost no lube at all; and it is only a matter of time before they do stick

note: ratio corrected
still a good way to pick up sticky valves

[Mitch//pa]

Is your car running ok? I never used a vacuum gauge for diagnosing or determining anything... There are better more modern accurate methods.
The only reason I own one is to use the pressure side for mechanical fuel pumps

[Fred S]

Originally Posted by tbirdtbird

For kicks, we assume you are putting MMO in the tank (4 oz per gallon)?

I think he means 4 oz. per tank.

[Dollar Bill]

Vacuum gauge readings give you another diagnostic tool when trying to determine faulty run conditions.

Chart below may be helpful with interpreting vacuum readings.

As Tbird indicated, vacuum signal is not quite as stable as 6 or 8 cylinder but anomalies should be apparent.

[Bob-A]

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Dollar Bill,

I run a Moto-Meter made vacuum gauge attached next to the steering wheel of my '31 roadster. Thanks for the chart info. Now maybe I can figure out what it is telling me beside just looking neat. The car is running great right now and the gauge readings are very different. Then
when it was not running so great. I'm sure the new intake/exhaust manifold gasket really helped.

Bob-A

[spinelll]

Originally Posted by Mitch//pa

Is your car running ok? I never used a vacuum gauge for diagnosing or determining anything... There are better more modern accurate methods.
The only reason I own one is to use the pressure side for mechanical fuel pumps

Car running ok. Just thought I'd check it out.

[CarlG]

My dad use to like having a vacuum gauge so that he could "keep his foot out of it" in order to get better gas mileage. I've had a couple vehicles with vacuum gauges as well for that same reason.

I rented a U-Haul truck several months back that had a vacuum gauge in it. Their instructions said pretty much the same thing, stay in the green for better gas mileage.

[rocket1]

My dad use to have a steering column mounted vacuum gauge on his 54 chevy,if you kept the needle in the green supposedly you got better gas mileage

[hale1776]

Ford installed vacuum gauge at factory mounted it on windshield so it could be seen easily he put rubber on the needle so wouldn't scratch glass. Checking vacuum is as simple as moving switch to activate gauge, indicator needle completely dependent on vacuum, fast movement indicates high vacuum usually only experienced going down hill with foot off the gas. Going uphill is when the indicator normally stops.

[Bob-A]

1931 Flamingo wanted a pic of my Moto-Meter vacuum gauge set up mounted on my '31 roadster. I couldn't figure out how to do it via a PM,
so I'll show it here.

Bob-A

[1931 flamingo]

Thanks big time.
Paul in CT

[captndan]

Somewhere there was a post about checking for a vacuum leak with a propane torch. Anyone know more about that?

[Tom Wesenberg]

Originally Posted by captndan

Somewhere there was a post about checking for a vacuum leak with a propane torch. Anyone know more about that?

That's how I've been doing vacuum checks since the 70's. Just open the propane valve a little, but don't light the torch, then move it around the intake manifold, and if the engine speeds up or smooth's out it means it's sucking in the propane.

[Mitch//pa]

I smoke test for vacuum leaks with my evap machine