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stevep516

Help with Vacuum Tank Fuel System

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I am struggling with the fuel system on my 1919 Bush. I understand the vacuum tank that provides fuel is the same as a Franklin. I have diagnosed every part of the system and cannot find anything that would creat a problem.

My question, does anyone have any info such as sketches or drawings that help explain the operation and the design concept.

It sounds like it sould be pretty simple, but the internal parts of the tank are full of rods, springs, float, and linkages.It doesn't quite make any sense.

I'd just like to get it fixed...........

Any help would be greatly appreciated.

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I am not familiar with the Bush vacuum tank. The one on my Chevy is a Stewart. They can't be that much different however. Heck, yours might be a Stewart also.

Vacuum tanks are very simple devices. There isn't anything really complicated about them but on the other hand it takes very little to make one cause grief.

I would start by checking the vacuum lines. This is where most problems can be found. Make sure they are tight and there are no leaks whatsoever. You might also check the fuel line to see if there is any trash in it.

If none of the above works contact me and we'll try something else.

Where the fuel line screws into the vacuum tank there should be a screen filter. There is on mine any how. Make sure it is clean. While you're checking filters, if you have one, make sure the filter in your carb is clear.

On the bottom of my vacuum tank is a small plug that can be removed to drain the fuel from the tank. Back in the day the books recommended that the vacuum tanks be drained every three months to remove any trash that may have accumulated. Gas was not as clean then as it is now.

Some vacuum tanks need to be primed before they will work. You might try putting a pint or so of gas in it to see if that helps. You should be able to do this by using a small funnel inserted in the top where the fuel line goes.

If that doesn't work it's time to look inside. You should be able to disassemble the tank w/o removing it from the car. Take the top off carefully. Try and save the gasket. You may need it to use as a pattern to make another. Inspect the gasket and see if it is torn and would have made a good seal. If the seal isn't good the vacuum would be unable to pull gas from the fuel tank.

The upper part of the vacuum tank has a float. These floats are known to leak. To check it you might first simply shake it and listen for fuel in it. If you don't hear anything then heat some water and put the float in the water. If there is a leak you will see bubbles come from where the leak is. A good radiator shop should be able to solder and leaks. I wouldn't recommend trying it yourself, there's apparently an art to it.

Now would also be the time to check the linkage the float was attached to. It should move freely but very slightly. I cleaned all my internal parts with B12 carb cleaner. There is a clearance on the linkage where the float attaches. It isn't much. IIRC it's about .02 or something like that.

The inside of the vacuum tank has 2 chambers, an upper and and a lower one. Remove the upper one. Inspect and if necessary clean the inside of the vacuum tank.

On the bottom of the upper tank is a small valve. Nothing complicated about it at all. It simply hangs there. Make sure it is clean and in good repair. Make sure it moves freely and forms a seal when in the closed position.

At this point, assuming the vacuum tank is attached to the car, put some gas in it and see if the car will run. It should be able to run for about 7 minutes +/- with just the fuel in the vacuum tank. If it does then you know the carb is good.

Reassemble the vacuum tank making sure all lines are fitted properly and there are no leaks. Make sure the gasket fits well. Be sure the screws are snug. It might be a good idea to prime the vacuum tank before putting it back together.

Once upon a time I was having problems that I couldn't pin down. Briefly, the car would run for awhile and quit for no known cause. It would then start right back up and do the same thing again.

In an attempt to trace it down I put a temporary hose, clear so I could see through it, on the fuel line just before it attaches to the fuel tank. This way I could see if the vacuum tank pulled fuel from the gas tank. You might consider doing this.

Vacuum tanks are very efficient. I would not recommend using an electric fuel pump. They are more trouble then they are worth. I know, I tried one for awhile.

Someplace I have literature on the Stewart vacuum tanks. If you want, I can find it and send it to you. I have no idea how different, if at all, they are from the Bush vacuum tank.

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Steve, if you're planning on attending AACA meets and having the car judged, you may want to consider adding an electric fuel pump. According to our rulebook, they are permissible for pre war vehicles, and it would solve a lot of your headaches.

If you choose to install an electric fuel pump, and point judge your car in AACA, just remember to install it in a manner to where it doesn't look out of place (orange wires, bright colored fuel pump, switch styles, etc.)

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I will personally buy and drive to Va and install a rebuilt vacuum tank before I allow him to put an electric fuel pump on that car. smirk.gif

Ok, I won't. frown.gif

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My personal experience with vacuum tanks on a couple of cars has been good. Once you understand them and get your system right, they are simple and trouble-free. In fact, they are more reliable than electric fuel pumps, which have to be replaced every couple years and can cause the older carburetors to flood from the pressure they create.

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You need a pressure regulator to go with an electric fuel pump.

I agree, an electric fuel pump is more trouble then it's worth. Kinda takes away some of the fun of having an old car too.

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Steve; Bill makes a lot of sense; i.e. especially when he states that the vacuum tank is normally a very efficient and trouble free fuel delivery system. Get yourself a Dyke's automotive manual, you'll find it completely covers the trouble-shooting and repair of all vacuum tanks, plus the added bonus that you'll find it a great repair manual for all other aspects of your car.

Incidentally, the problem doesn't have to be just the vacuum tank. I once ground the valves on a '26 Marmon, replaced the head gasket and head. Hooked up the vacuum tank line to the intake port in the head, and away I went. I ran well for a couple of hundred miles and then started starving for fuel.

Well, no surprise when it was found that no longer was there enough vacuum being created to pull fuel into tank; this due to the head bolts having to be re-torqued once the head gasket seated itself, vacuum was lost due to this phenomenum. This re-tightening done, low and behold, increased vacuum, enough so that the tank again functioned properly all by itself.

regards; oldiron

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One of the subtle things - and less obvious to troubleshoot - about the vacuum tank is the operation of the vent. Often when a new gasket is fitted, the small hole that vents the lower (outside) tank becomes plugged. If this happens, the tank will not work as the gas cannot dump from the upper (inside) tank to the lower unless the vacuum vents. This vent hole is always open, but on most tanks, vents into the top casting near the vent valve for the inside tank.

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I had forgotton about that vent hole. Glad you mentioned it.

Another thing I forgot is that the gas tank needs to be vented. Mine has a small, maybe 1/16" hole in the gas cap. If it's clogged the vacuum tank can't pull fuel from the gas tank.

When I had problems with mine I simply removed the cap to see if the vacuum tank worked any better.

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Guys,

I appreciate all of the input. I'm kinda a original type guy, so I'm going to try and solve the vacuum tank issue. It's Thanksgiving week and I'm on vacation so I can't think of anything better to do. It's 73 degrees outside and the sun is shining, I'm heading to my "mancave".

Happy Thanksgiving!!

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Gents,

I followed everyones advice and checked out the system.

The vacuum system when measured at the fuel inlet side of the tank is pulling about 5" of Hg. This appears to awfully weak............

Any comments?

Steve P

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Check the gaskets around the intake manifold and the carb. Double check the fittings around the vacuum line to the vacuum tank and manifold.

I have no idea what the vacuum should be where you measured it but I would think it should be at least 16" or more. Can you check the vacuum elsewhere?

Get back to me on this before you have T-day dinner. I'm curious to know how it turns out.

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Lots of good advice here....

One more thing to check is the pot metal top of the vacuum tank. Very small (hard to see) cracks may leak air. Simply coat the inside of the lid with gas compatable sealant (Crazy Glue works).

Also, make sure all the fuel lines are sealed and the gas tank is vented.

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Cussing at mine has never worked but threatening to put a F*** engine in it does the trick every time. smile.gif

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I have three cars with Vacuum tanks on them and they all work once you have a good vac and with no leaks. The biggest problem I have found is the gasket on the intak manifold. If it is bad or the manifold warped it will never work but it will work when set up correctly. Have a nice Christmas.

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Mine works fine. I had trouble starting out with a rebuilt one that was flawed and I didn't catch it. One time after that I had a float that leaked. These are normal and probably happened when new. Other than that they do just fine.

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Just to echo others' comments, a vacuum fuel pump works fine (mine is an Autovac but it is very similar to a Stewart), provided there are no leaks in the vacuum lines. I once removed the vacuum-operated windshield wipers leaving the tiny pipe end open, took my girlfriend's 93 year old mother for a spin, and five miles down the road the engine stopped. No fuel! And yes, to make the pump work again, I had to prime it by removing the feed pipe and pouring gasoline in.

However, enlarging on a point made by someone else, unlike an electric pump which obviously doesn't deliver fuel under pressure when it is turned off, a vacuum tank has fuel in it permanently, so the needle valve in the carburetor float chamber is permanently under pressure. Even if the valve is in good order, it is almost bound to leak slightly over hours or days, whereupon the chamber overflows. Thus it is very desirable to have a faucet in the gravity feed from the tank to the carburetor, and to turn it off when the car is left for any length of time. I have twice woken in the middle of the night, smelled gasoline, and had to go down to my basement/garage to turn off the faucet (and it was dangerous since there are two gas pilot-lights there too).

Ken G, 1925 Rover 16/50 (San Francisco)

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Another source of aggravation on the Stewart units is the fuel line inlet fitting to the tank. Too heavy a hand tightening the tapered brass fitting into the die cast top cap will cause a tiny crack in the cast piece, allowing vacuum to "escape".

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Steve, 32 dictator has my answer. The clogged vent line is one of the most common problems with vacuum tanks. These are simple and efficient units that are dependable when working properly. Remember it only takes approximately 3 inches of mercury to make them work. a normal engine of the 20's produces 14 inches of vacuum. Even with vacuum leaks the unit should function well.

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If I can make a small sidestep here - my Maxwell Vac tank has vacuum drawn from the oil pump, the advantage there is that if you run out of oil you will also run out of fuel, also it doesnt matter how many hills you climb or how wide open the throttle is the vacuum supply is always there. Forward thinking ?

chris h

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Just joined then logged in, but lost the thread I was reading on rust in the fuel tank. I'll put the tip here, cos dinner is nearly ready and I want to give a cure for rust. Rust in fuel tanks, etc. Apart from molasses (Idon't know about it but I have heard good tales), use a counted handful of nuts and bolts and rattle tank to loosen big surface rust pieces which are almost loose. Count nuts and bolts out. Rinse tank with water and all debris, put in sun for a week, vent upwards. Now mix shellac and metho like French polish, say about a litre (in Australia) a few pints for the USA. Put in tank, shake, put shellac/metho bag in jar. Put tank in sun for a week. Re-apply French polish coating two more times or whatever. Petrol does not effect shellac. Rust dust blocks lines, filters, jets, goes into engine as fine metal pieces. Clean fuel lines, coated in shellac, vac tanks (some I have rusted through), etc. Rust causes a cylinder to miss if the plug whiskers. My VF750 Honda circa 1980s had fine rust in the carburettors and jets, even though all fuel goes through a paper fuel filter after an electric fuel pump (probably why), simply from surface rust in the tank.! Shellac all surfaces which may put rust in fuel and careful where the filter is where a vac system is used or electric pump.!

Spread the tip, but especially not to T owners!

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