Stewart Vacuum Fuel Tank Advice Needed

[Kfigel]

Wanted to confirm that my vacuum fuel tank should be seeing about 3 to 4 inches of vacuum from the engine of my '22 Studebaker Big Six upon startup - this should be enough to start the flow of gas from the gas tank, correct?  (Starting with an empty fuel tank). Should then see about 12-14 inches of vacuum once the engine is running, correct?  To bench test the fuel tank (using water, not gas) I could run a variable vacuum pump at both vacuum settings, say 3 inches and then 12 inches, and should see the tank drawing water, correct?  At each setting, 3 inches and 12 inches of vacuum, would the suction of the water be intermittent as the rising float in the internal vacuum canister closes the vacuum valve until the water drained into, and then out of, the outer tank as if going to the carb?  This would show that my fuel tank is working properly?  

Edited May 11 by Kfigel (see edit history)

[Mark Shaw]

Just measure the vacuum at the intake manifold.  Forget using water, it is heavier than gasoline and may not provide a reliable result.  The primary issues with these vacuum fuel pumps are leaks in the seals or corroded fuel lines from the gas tank.  

[edinmass]

 

Are you asking will the car draw fuel from the tank with the S-W unit empty? The answer is no.......you must prime it. 

[nat]

     Try this.

     Make sure the line from the intake manifold and the fitting from the intake manifold to vacuum line, (which make be intentionally restricted, don't drill it bigger), is clear.

     Shut the vacuum tank bottom valve for carb feed off, rig up a gravity fuel feed to the carburetor and connect the vacuum tank fuel suction line to a can of fuel with a transparent hose.

     Start the engine and see if fuel is drawn from the can of fuel.  If not, plug the vent pipe with a finger and see if that makes a difference.  If it does, the vent valve isn't sealing.  If not, you have leaks.  Either pin holes or gaskets. 

     If it without plugging the vent it  stops sucking fuel from the supply when the vacuum tank is full, the flap valve may be at fault.

     Experts:  Correct me where I'm wrong.

Nat

Edited May 12 by nat
. (see edit history)

[pmhowe]

While you are going through this process, also check your float.  I was recently dealing with a rough running problem with symptoms of flooding and then fuel starvation. It turned out to be a combination of crud sometimes plugging the fuel  line and a vacuum tank float that had developed a pinhole leak. The float was slowly sinking. It may not be the cause of your current problem, but please check your float. There should be no gasoline inside it

[Kfigel]

19 hours ago, edinmass said:

 

Are you asking will the car draw fuel from the tank with the S-W unit empty? The answer is no.......you must prime it. 

Thanks, in my way that was what I was asking.  Didn't know if the initial vacuum the tank would see upon startup would be enough to start the flow of gas with an empty fuel tank.  I'll make sure I have it primed when I put it back on the car. 

[Kfigel]

20 hours ago, Mark Shaw said:

Just measure the vacuum at the intake manifold.  Forget using water, it is heavier than gasoline and may not provide a reliable result.  The primary issues with these vacuum fuel pumps are leaks in the seals or corroded fuel lines from the gas tank.  

Thanks, when I bench test it I'll plan to run the vacuum at about the 12-14 inches it will see when the engine is running. No water.  

[Kfigel]

9 hours ago, pmhowe said:

While you are going through this process, also check your float.  I was recently dealing with a rough running problem with symptoms of flooding and then fuel starvation. It turned out to be a combination of crud sometimes plugging the fuel  line and a vacuum tank float that had developed a pinhole leak. The float was slowly sinking. It may not be the cause of your current problem, but please check your float. There should be no gasoline inside it

Thanks, will do this. 

[Kfigel]

On 5/11/2024 at 8:04 PM, nat said:

     Try this.

     Make sure the line from the intake manifold and the fitting from the intake manifold to vacuum line, (which make be intentionally restricted, don't drill it bigger), is clear.

     Shut the vacuum tank bottom valve for carb feed off, rig up a gravity fuel feed to the carburetor and connect the vacuum tank fuel suction line to a can of fuel with a transparent hose.

     Start the engine and see if fuel is drawn from the can of fuel.  If not, plug the vent pipe with a finger and see if that makes a difference.  If it does, the vent valve isn't sealing.  If not, you have leaks.  Either pin holes or gaskets. 

     If it without plugging the vent it  stops sucking fuel from the supply when the vacuum tank is full, the flap valve may be at fault.

     Experts:  Correct me where I'm wrong.

Nat

Thanks, will be doing this.  

[Stude Light]

There is a great write up in the May-June 2024 edition of the Antique Studebaker Review (Antique Studebaker Club's periodical) on the Stewart Vacuum Tank Fuel Pumps. It starts with a reprint of Bill Gannon's article titled "How to Live with Your Vacuum Tank" originally published in the April 1981 edition of the Review and followed up with an article by Mike Margerum. 

 

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