retrorocket

27 chevy vacuum tank/fueling issue

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I am helping someone with a 27 chevy truck that is having a fueling issue.

 

Background info: it has the original  4 cylinder engine that utilizes a stewart warner  vacuum tank (the taller skinny one) to get fuel to the carb.  After being in storage  for several years it was time to get it running again. Gas tank was previously sealed with a gas tank sealer that decided to become a big ball of gunk in the bottom  of the tank. When last run, the vacuum tank and carb were completely drained and on inspection were completely clean and free of any gunk. due to the condition of the gas tank, it was replaced with a boat tank with a plastic tank with vented gas cap. When i got there the engine started right up and ran like a top several times, and ran for a about 5 minutes each time. The last time it ran for a little longer. We went to lunch and came back and fuel was seeping out of the vent on the top of the tank. We drained the vacuum tank checked over the lines, removed the check valve at the gas tank, and restarted the  truck, drove it for about 10 minutes and parked it. fuel line was leaking a little bit  just downstream of the gas tank so we fixed it, and restarted it. now the truck will run for about  a minute or so and die. It sets for about a minute and will restart, run for about a minute and then start again, run for a minute  and die again. 

 

Process of elimination, the carb was removed, checked over and reinstalled. no change.  Fuel filter is about 2/3rds full when running. Removed gas cap from fuel tank to make sure it is venting, still no change. Next day while i am not there, they put a rebuilt carb on it, no change. Removed fuel tank and directly gravity fed the carb, truck ran until they shut it off. Pulled top off the vacuum tank, inspected it, said nothing appeared to be blocked or broken and ran the truck  with just the fuel in the vacuum tank and it ran like a top  for a long time, until they shut it off.  Put the top back on the vacuum tank, started the truck, it again runs for about a minute and dies. Fuel filter has gas in it, carb bowl has gas in it,  but it won't stay running. While it is running there is a steady stream of air bubbles  entering the fuel filter, but the filter remains over half full, with the outlet side fully covered with gas. 

 

All of this seems to point at something wrong with the vacuum tank, but not sure what would be causing this. It seems as though something is keeping fuel from flowing- like there is vacuum leak somewhere that is keeping the fuel from flowing while running, but  i am not sure where to start tracking this down.  

 

We are committed to keeping the vacuum tank and not putting in an electric fuel pump. 

 

Any suggestions from folks who know more about this setup?

 

Thanks in advance!

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Yeah sounds like the valve/springs/levers in top part of the tank are dodgy, assuming there`s no cracks in the casting ??

 

As mentioned, plenty of how to`s with pics on the forum; probably start with searching "stewart warner"

 

Be careful with installing an electric pump as they usually generate 2- 3 psi, vac tanks deliver 0.5 psi, any more than this and the float valve wont be able to stop the resultant flooding.

 

One quick check you can make to see if the vac unit is drawing fuel, is to put some fuel into the vac tank, close it up and get the engine running, place your hand on the upper vac tank casing and see if there`s a temperature change from time to time. The logic behind this is, as the fuel is emptied from the vac tank, the internal float mechanism will periodically drop and open the suction port to the main fuel tank, there will then be fuel flowing in to the vac tank and (yes believe it) you can actually feel the temperature drop as the fuel flows through the inlet port, once the float rises and shuts off fuel flow you can feel the loss of cooling. If you have good hearing or put a probe between your ear and the mechanism you can also hear the "clicking' of the valve mechanism at the same time. 

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I think you need to go back to the way the car was built and that is remove the fuel filter, remove the plastic gas tank, remove the fuel pump.  The vent should not have fuel coming out of it which sounds like the electric pump pushing fuel after being shut off.  It sounds like you are only running a carb bowl of fuel at a time and your carb float may not be set at the right height or the needle valve may be sticking.

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7 hours ago, jan arnett (2) said:

I think you need to go back to the way the car was built and that is remove the fuel filter, remove the plastic gas tank, remove the fuel pump.  The vent should not have fuel coming out of it which sounds like the electric pump pushing fuel after being shut off.  It sounds like you are only running a carb bowl of fuel at a time and your carb float may not be set at the right height or the needle valve may be sticking.

The truck does not have a fuel pump. We have checked the height of the float, and the carb bowl has fuel in it when it dies, ( or more accurately, immediately after it dies).

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Posted (edited)

Hchris, we know that the vacuum tank is filling with fuel. The last time we tested it it died we took the top of the vacuum tank off and the outer tank had plenty if fuel in it. We then started it, and the engine ran for several minutes off from that fuel in the vacuum tank until we turn it off. Once you put the vacuum tank back together and restart it it will only run for about a minute and then die.

The pressure that you stated is one of the reasons we don't want to go to an electric fuel pump. We would need a regulator to get it down to one PSI or less. 

Edited by retrorocket (see edit history)

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20 hours ago, Stude17 said:

This post has lots of suggestions and a good diagram.

 

vacuum tank problems

By olympic, April 1, 2018 in General Discussion

Thank you! I did a search for vacuum tank but didn't think about doing a search for Stewart Warner

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Ahh these vacuum tanks can be hours of fun !😁 so I would be checking the gasket on top of the tank also check that the vent valve is clear and working correctly on two occasions this has caused me grief once when it was not clear and once when it was not sealing correctly when it should and that was caused by a little brass seat being missing installed that and problem solved. I have found with these tanks you have to be methodical in check every thing and not be distracted. Good luck

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I don't think you have a fuel problem.  When the engine dies you say it has fuel in the bowl,  a fuel problem would not have a fuel bowl full.  Have you checked for spark when it dies.  A condenser can be problematic. Have you checked the gaskets between carb and intake and the vac line between intake and vacuum tank.  You really got me grasping AT IDEAS..  

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3 hours ago, retrorocket said:

Thank you! I did a search for vacuum tank but didn't think about doing a search for Stewart Warner

Have a look at this post

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Retrorocket the problem I suspect is that the vacuum is not being cut off to the vacuum tank when it is full causing fuel to be drawn from the tank along the vacuum line and into the inlet manifold and flooding the engine with fuel.  This is generally caused by the brass seat for the cut off needle becoming dislodged from the diecast vacuum tank top and not allowing the needle to seat properly and cut off the vacuum.  The engine will simply not run when flooded with fuel in this manner and that is why it dies after about a minute and fuel is coming out of the overflow.

 

I have had this problem myself and to correct it I machined a slightly oversize brass seat, however, I have heard of locktite being used to ensure the brass seat stays in place.  Sometimes it is difficult to see the dislodged seat as it goes back in and comes out periodically.

 

I have heard of engines needing new crankshaft and rod bearings due to the dilution of oil by the fuel.

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I had a problem with a loose vacuum valve seat.

I discovered the loose seat purely by accident when I was operating the mechanism.

In my case the fit was a perfect slip fit which was easily remedied with Loctite.

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1 hour ago, cahartley said:

I had a problem with a loose vacuum valve seat.

I discovered the loose seat purely by accident when I was operating the mechanism.

In my case the fit was a perfect slip fit which was easily remedied with Loctite.

 

Yes I think Loctite is the way to go as it saves removing/replacing pins from brittle diecast metal fulcrums which are very easy to break.  It would have saved me a lot of time replacing the fulcrum I broke.

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