1922 Big Six Engine Vacuum Leak

[Kfigel]

Looks like I've got a vacuum leak in my engine.  I'm reading 4 inches Hg at the intake manifold; Stewart canister not getting any gas as it is a vacuum fuel pump.  Anyone know if the original design vacuum for my car is 18-22 inches Hg; if not, do you know what it is?  Thanks

[Stude Light]

I would expect that it should read something north of 15 in Hg at an idle. 4 is way low.

 

To find a leak, I use a flammable spray such as carb cleaner or starting fluid and just use short bursts around each connection or gasketed area and when you hear an increase in engine rpm you have found the culprit.

[Kfigel]

1 hour ago, Stude Light said:

I would expect that it should read something north of 15 in Hg at an idle. 4 is way low.

 

To find a leak, I use a flammable spray such as carb cleaner or starting fluid and just use short bursts around each connection or gasketed area and when you hear an increase in engine rpm you have found the culprit.

Thanks, Scott.  Given the age of the car I thought I should be seeing a value approaching 18 inches, but wasn't quite sure what it might be around. 

[Axial_Flow]

How well is the engine running in this current state of low manifold vacuum?

 

With such a low reading, I suspect a leaking or stuck open intake valve or serious loss of engine compression.

 

Please report your findings

[Kfigel]

29 minutes ago, Axial_Flow said:

How well is the engine running in this current state of low manifold vacuum?

 

With such a low reading, I suspect a leaking or stuck open intake valve or serious loss of engine compression.

 

Please report your findings

Well, the car actually won't run at all with such low vacuum because it has a vacuum fuel pump.  4 inches is not enough to draw any gas into the canister.  I did prime the canister with gas and the car did start and run until it ran out of that gas.  During that relatively short time the engine ran very rough.  I should add that I initially had 1" of vacuum and heard the tell-tale "pisst" sound of rushing air.  I then resealed the six priming cups connections, and that got rid of the sound and increased the vacuum to 4".  Looks like there is a significant leak elsewhere.  

[Axial_Flow]

43 minutes ago, Kfigel said:

Well, the car actually won't run at all with such low vacuum because it has a vacuum fuel pump.  4 inches is not enough to draw any gas into the canister.  I did prime the canister with gas and the car did start and run until it ran out of that gas.  During that relatively short time the engine ran very rough.  I should add that I initially had 1" of vacuum and heard the tell-tale "pisst" sound of rushing air.  I then resealed the six priming cups connections, and that got rid of the sound and increased the vacuum to 4".  Looks like there is a significant leak elsewhere.  

Understood

 

Rule out the easy vacuum loss sources first, I tend to think you have valve issues.  Removing the tappet cover would give quick access to assess the valve action.

[Kfigel]

34 minutes ago, Axial_Flow said:

Understood

 

Rule out the easy vacuum loss sources first, I tend to think you have valve issues.  Removing the tappet cover would give quick access to assess the valve action.

Will do. 

[J Tryloff]

My 23 special six had a lot of leaking around the spark plugs and where the intake manifold seals to the engine. 

[Kfigel]

12 hours ago, J Tryloff said:

My 23 special six had a lot of leaking around the spark plugs and where the intake manifold seals to the engine. 

Thanks, I'll take those on next!