1920 Stewart Vacuum Tank Issue

[kfle]

I have a 1920 Cole with a Stewart special Cole vacuum tank which was high volume.  I rebuilt it not long ago as it was completely gummed up from previous owner leaving old gas in it.  When I get the car running it pulls gas from the tank and cycles correctly.  However after I stop the engine and let it sit for the day the vacuum tank empties itself of gas and the gas runs back into the gas tank.  This means that I need to refill the vacuum tank manually to get the engine started as it can’t pull enough fuel from the tank into the empty tank to start the fuel hungry V8.  Any ideas on what would be causing this and how to correct it? The gas cap on the gas tank is vented correctly.   
 

Here is a video of the engine running so you can see the vacuum tank. 
 

 

[edinmass]

Easy. You need to shut off the petcock every time you park it. Sometimes it’s a leaking float in the carb causing the issue. Try first shutting it off. My White will hold a month without issue, my Cadillac was good for a day. Our V-16’s get turned off EVERY time we drive them. 

Edited September 25, 2021 by edinmass (see edit history)

[wayne sheldon]

Ed M snuck in on me. So a slight change. His suggestion first was also my first thought. Then if that doesn't solve it?

 

Most likely? There is a "flapper" 'valve'  where the fuel in the upper tank drains into the lower tank after the upper tank has been filled by the vacuum switching. IF (my big IF) the flapper valve isn't a nearly perfect flat fit on the outlet fitting? It could be possible to syphon back. It really shouldn't IF (another big IF) the upper switching mechanism is working properly and the upper mechanism's vent isn't blocked. So both the upper vent AND the lower flapper valve need to be checked. 

Often, the lower flapper valve can be touched up using very fine (like 600?) wet or dry sandpaper. Draw the paper through with only slight finger pressure holding the flapper closed over the paper. Both the fitting and the flapper need to be dressed a bit.

If that flapper is off much at all? The vacuum tank won't work at all because the vacuum pressure will draw fuel from the lower tank instead of the fuel tank. Under vacuum pressure, the flapper valve could pull tight enough to draw fuel from the rear tank, but leak fuel back when the vacuum is cut off.

 

Generally speaking, fuel should NOT be able to syphon back, for a variety of reasons. But it can happen. But try Ed M's suggestion first.

[wayne sheldon]

By the way, Kevin, haven't seen you on here in awhile. I hope all is okay?

[HarryLime]

There is always an air space in the top of the tank . The gas cannot siphon back to the fuel tank . Take the supply line off the vacuum tank after running the car . Is the vacuum tank empty or full ? 

[wayne sheldon]

Been out cleaning up the barn for a couple hours. The more I thought about it, the more sure I was that any syphon would be broken before the upper chamber was empty. So, although it is possible for them to syphon back maybe half the vacuum tank's volume? It cannot empty the vacuum tank beyond that point. So a syphon event should not prevent having enough fuel to start the engine. 

Go back to Ed M's shut off the fuel, and as long as there isn't a leak in the bottom of the vacuum tank or the shutoff valve or connections? One should be able to start up any time for days. I have had a few cars with vacuum tanks. Most of them with the fuel shut off under the vacuum tank, could hold out for weeks and be started without priming the tank.

 

And I am not editing out my foolish incomplete thought. I leave my mistakes for all to see rather than cause confusing threads .

[cahartley]

My dad imprinted upon me to always shut off the gas no matter WHAT when it's possible to do so.

It's also good to shut off the gas and run the carburetors empty too at season end.

 

[mrspeedyt]

maybe it’s just the modern gas evaporating? this modern gas ain’t worth a sh….. bit.

[old car fan]

The fuel  doesn't  get high enough  in the tank to siphon. 

[nearchoclatetown]

As others have said, the problem is not in the vacuum tank, it's in the carb. Gas can't syphon back to the gas tank. It is leaking past the needle valve in the carb.

[edinmass]

Check the float to be sure it has enough to seal the needle and seat. If it’s cork, toss it in the trash. I won’t use the modern plastic material that they sell. I make brass floats from scratch. E10 is less dense than gas of the 20’s to 80’s, so float height and mixture MUST be accounted for. Idle circuits in newer carbs must also be modified. Almost no one ever does it. It’s hard, and easy to ruin carbs. And, while your at it, recurve the ignition.......if you have a modern rebuilt engine.

[kfle]

17 hours ago, edinmass said:

Easy. You need to shut off the petcock every time you park it. Sometimes it’s a leaking float in the carb causing the issue. Try first shutting it off. My White will hold a month without issue, my Cadillac was good for a day. Our V-16’s get turned off EVERY time we drive them. 

Ok I will have to try that.  My other Coles don’t require me to do it, so didn’t think I would need to.  

[kfle]

17 hours ago, wayne sheldon said:

By the way, Kevin, haven't seen you on here in awhile. I hope all is okay?

Yes all is good and thanks for asking.  Just been extremely busy and haven’t had as much time for the cars as I would like!

[kfle]

6 hours ago, edinmass said:

Check the float to be sure it has enough to seal the needle and seat. If it’s cork, toss it in the trash. I won’t use the modern plastic material that they sell. I make brass floats from scratch. E10 is less dense than gas of the 20’s to 80’s, so float height and mixture MUST be accounted for. Idle circuits in newer carbs must also be modified. Almost no one ever does it. It’s hard, and easy to ruin carbs. And, while your at it, recurve the ignition.......if you have a modern rebuilt engine.

Ok I’ll check the carb.  I never use E10 gas in the cars as 100% non ethanol gas is plentiful in west Michigan.  

[edinmass]

Remember, even a small drip or seep will drain a tank fast. Float is the most common issue. Check fuel lines and fittings. Cars that run hot can boil fuel out of the bowl, causing fuel to flow out of the tank and evaporate, leaving no signs of leaks.