Vacuum tank woes

[WPVT]

I rebuilt the vacuum tank on my 1929 White and then it was working fine, but now it has developed a problem. I'd like to approach the problem logically, before I take the tank apart. When I rebuilt it, I could see that it was in fine shape, just had dried out gaskets.

While the engine is running, the vacuum tank runs dry, i.e., no gas coming out the bottom. It has sufficient vacuum, and there is no obstruction between the vacuum tank and the gas tank. Since it was working OK, I'm guessing that the flapper valve is working. Am I correct that the float must be stuck in the upwards position, or at least the valve it actuates is stuck closed? I can add gas through the priming port on the top of the vacuum tank, and the truck runs until that gas is consumed.

Intermittent problems can be tough to solve, which is why I'd like to think this through while the tank is dry and not working. Disassembling the tank will probably cause whatever is stuck to loosen, and the problem will remain a mystery.

Here's another question...If the float mechanism is functioning correctly, the float should be down while the tank is dry. When I fill the tank through the priming port, I should hear it click at some point, right? I would think that if it doesn't click, then either it isn't working, or it's stuck in the up position.  

Thanks in advance. 

[Friartuck]

When you hear it click meaning the float has risen to a point where it should be shutting off the vacuum (not drawing fuel from the tank) and releasing the fuel into the main part of the tank and on to the carb. If the flapper gasket is not working properly, the vacuum in the inner chamber (tank) is also trying to draw fuel into the inner chamber which it should not. That is defeating the purpose. Check that you don't have a vacuum leak in the lid assembly. (crack in the top tank assembly, etc. Are you sure there is vacuum present on the fuel line (from the tank)? Run the vehicle by priming the tank the way you've done and check for vacuum sufficient to draw fuel from the tank. 

StewartWarnerVacuumTank2-11-27.pdf

Edited May 19, 2018 by Friartuck (see edit history)

[cahartley]

Check to make sure the vacuum valve (both actually) in the tank cover is firmly seated and working.

I had an intermittent problem as you are having and discovered, by accident, the seat was actually falling out of the top housing....... 

A drop of Loctite fixed it.

Also you likely have the later tank in which the inner tank has a very narrow flange.

That tank uses one CORK gasket which goes between the inner tank flange and cover.

[WPVT]

Thank you both for your thoughts. 

I'll try filling the vacuum tank through the port, running the engine, and checking the line to the fuel tank for vacuum. I'm guessing I don't have any. If that's the case, it would mean that the float and/or spring mechanism is stuck in the upward position,  closing the vacuum valve and opening the atmosphere valve, correct? 

I think I can rule out things like bad gaskets, casting cracks etc., since the vacuum tank was working fine before the truck sat idle for a month. 

I suppose I could disassemble the tank very carefully and hope that the problem will be visible when I peek inside.  Maybe I'll be able to see if something is hung up in the spring mechanism.  I tested the flapper valve when I last had it apart, so I know that works OK.

 

[DavidMc]

I think I can rule out things like bad gaskets, casting cracks etc.

Maybe not, the pot metal top can fail at any time.   

I had one where the small brass  valve seats came loose in the pot metal and the tank ceased to work because it could not hold the vacuum.   Fine cracks at the threads can also occur some time after tightening the fittings.  Old pot metal  can be very weak.   

[WPVT]

Thanks. I'm sure I could be wrong about that. Just trying to work through the probabilities. 

 

 

   

[cahartley]

^ As I mentioned above it was by shear luck I found the problem.

I was holding the assembly over my head and working the float up and down repeatedly.......until ONE TIME I noticed the needle seat had dropped out of place....... 

[Wheelmang]

With the exception that you say it was running fine after you reassembled you are describing the exact issue I had on my 26 DB. Did it run for an extended period after reassembly or just until the initial prime ran out? It wasn't until numerous disassembles that I discovered the alignment needle on the bottom of the float was not in the hole at the bottom of the tank. The result was the float was slightly cock-eyed in the tank and thus was assembled with the float stuck in the up position thereby shutting off the fuel supply. Mine is working perfectly after correcting that. 

 

[cahartley]

^ That too!

It's not the easiest thing in the world to get it properly in place....... 

[WPVT]

Thanks to you both for your comments. Since rebuilding the vacuum tank, the engine ran at fast idle for 30 minutes or so on several occasions.  So it was working OK.

I won't be at the truck's location until later in the week.

I agree that it seems like the float and/or the valve it actuates is stuck in the up position.  Now I'm trying to remember if the priming port goes straight into the inner tank, so that I could possibly see or touch the float.  

[Friartuck]

I think there is a long pin at the bottom of the float that must be aligned into the bottom of the inner tank. If not aligned, it could easily get stuck in the high position.

[old car fan]

Just pulled one apart yesterday,inner tank had been bent ever so slightly,that the needle was binding in the inner tank.

[WPVT]

I took a close look at the vacuum tank this morning. By unscrewing the priming port, I was able to see that the float was not stuck in an upright position, it was down where it belonged. Good to know that the port can be used for a visual check on the float.

My next step was to check the little mesh strainer at the fuel inlet. It was plugged solid with some rust particles. So that was the problem. I'm creating a new topic to ask if anyone has successfully installed an inline filter between the fuel tank and the vacuum tank.  

[Layden B]

A filter in the modern sense may be too much restriction. A well designed sediment bulb that allows the particles to drop out by gravity should do the job.

[Grimy]

12 minutes ago, Layden B said:

A filter in the modern sense may be too much restriction. A well designed sediment bulb that allows the particles to drop out by gravity should do the job.

Yes, unless you have a dirty gas tank.  I've used inline filters successfully with vacuum tanks on two cars.  If you suspect a lot of crud in the gas tank AND have a 5/16" fuel line, the Fram G-3802 is a large capacity unit used on Ford vehicles for years and is available almost anywhere.

[Ltc4748]

Most auto parts stores have a glass center fuel filter that uses a fine screen to catch debris. The nice thing is you can visibly see if it is dirty and it easily comes apart to clean and put back together. I am using them before the Vacuum tanks and at the lowest point in the line with easy access to inspect. It has not interfered with the operation of any of the vacuum tanks yet for me. They cost about $10 and are 1/8" female pipe threads. They come with plastic fittings but I install brass ones. The filter is maybe .75" diameter and 2" long

 

 

 

[old car fan]

I restore and sell parts for the Stewart Warner. Also have rebuild kits.it is a hobby,not a job.at Hershey every year