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1925 Vacuum Tank


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I finally got frustrated enough with the electric fuel pump in my 1925-25. No mater what setting I had it at, down to 1

lb. ?? of pressure it was still flooding. I received the new float from Gregg Lange of the 1915-1918 News group on Friday. (Beautiful fit and finish!) I joined at the urging of Terry Wiegand since many of the issues I have are similar to the earlier vintage Buicks. The newsletter CD I purchased has information on the fuel systems I had found no where else. Gregg produces floats for other year Buick Marvels also.

I polished the needle on my lathe and with a dead flat jewelers stone to remove the slight ridge. Set every thing up and left the cover off to check the float action. All seemed well idling so I replaced the cover and went for a drive. Twice around the block it was popping and barely got it partially into the garage. Gas was shooting from the air horn on the carb!

I checked on line about the "Mr. Gasket" regulators. On one of the negative reviews (there were many) talked about on his unit the screws on the back of the diaphragm case were all loose. I checked mine and they too were loose. So that was the problem? I added small lock washers and checked the diaphragm and it looked good. Reassembled, tightened all screws and reinstalled. Within 2 minutes of running fuel was shooting out again. No mater what setting it was the same.

So... Today I finally plumbed in the vacuum tank! I had rebuilt it last year thinking I would get around to it this past summer. Also the philosophy that "if it ain't broke". I had been putting it off because the brass feed tube to the top of the vacuum tank fitting needed re-soldered. I redid that last night. I checked to see if the in-line electric pump would pass air and it did. So I left it in line. In case I need to fill the vacuum tank. With the feed fitting removed from the top of the tank I filled with a little over a pint of gas, opened the stop valve and started up. Put my thumb over the hole on the top of the tank and felt like it had pretty good suction. Removed and threw the regulator as far as I could! Coupled everything up with a high quality in line filter. Started up again and watched the float operation. The fuel level in the bowl was much lower than it was previously. Replaced the carb cover and took her out for a 5 mile drive. "Beulah" seemed much happier and no popping or starving. I still have to get the sweet spot on the carb adjustment as Beulah does not seem to have much power.

Now to the other issues such as cooling, inconsistent charging and that pesky sticking clutch.

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Larry,

Glad you are no longer relying on the electric fuel pump. Just make sure you shut off the fuel feed to the vacuum tank and run the engine dry before putting it away for winter. This will minimize the gasoline varnish build up on all the fuel system internals.

Also try to use non-ethanol fuel when available. She will be all the happier for it...

Edited by Mark Shaw (see edit history)
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Larry brings up a good point and one that is a little scary too. I've seen two fuel related old car fires. Both were related to electric fuel pumps and the fact that their minimum pressure is more than the old carburetor and float/needle can handle.

A vacuum fuel tank 12 inches above a Marvel carburetor creates about a third of a PSI in pressure. No electric pump or regulator can get you that low. Electric pumps exceed the inlet fuel pressure a vacuum tank type carb. was ever designed for.

For those who were not reading car magazines in Chemistry or Physics class while they were asking what's-her-face to be their lab partner, let's do the math.

1 PSI = 27.67 inches of water

Gasoline is ~75% as heavy as water

Let's assume the highest point the fuel level in your vacuum tank ever gets is mid-way, and from there to the top of the Marvel where the needle valve is, is 12 inches. Measure your car and plug in your own number.

(1 PSI/27.67 in H2O) x 12 in H2O = 0.43 PSI but gasoline is 75% the density of water so 0.43 PSI x 0.75 = .33 PSI

No wonder that 1 PSI pump is a causing gasoline past the float needle valve and into the carb. circuit causing flooding and rich running; it’s 3 times what the pressure should be. Worse, it can be forcing fuel out the vent on the top of the carb. bowl too, just looking for something to ignite it.

How did you all wire that pump? To the ignition? Get in a crash and everything stops but that pump you wired that keeps running if you don't turn off the ignition. You need to either ground it through an oil pressure idiot light switch that shuts off when there is no oil pressure (but also give it cranking circuit electricity and a diode so the pump does not engage the starter) or run it off the charging side of the generator with a diode too so the battery does not keep things running. But, you all get my point.

Or, fix that vacuum tank and be smart like Larry!

Edited by Brian_Heil (see edit history)
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Back in 1967 when I got my 1918-6-45 it had just an electric pump and I had constant flooding issues with it. I too thought about that head pressure issue too. Among the junk I got with the car was a gutted vacuum tank. This was my inelegant solution when my tools were not much more than a 1/4" drill and propane torch. post-38164-14314225407_thumb.jpg

Really crude!! Just junk from a '41 Plymouth carb, but it works - and still does. I still have the electric pump feeding the top as normal. It fills the vacuum tank about 1/2 full and the carb sees what it expects as far as fuel pressure. The carb has its original float, needle and seat and it works perfectly to this day with no leakage. But I still do turn off the tank when I stop for the day.

One of the nice things is that it all looks completely original with all its plumbing - I have the vacuum line from the manifold blocked.

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  • 1 month later...

I have been trying to send photos to Terry Weigand and Dean Tryon of what I had done with my Marvel to solve some issues. My explorer will not let me add the resized photo files. So I will make my case here. I still had the leaking issues and thought I would re-check the carb internals and make new gaskets. In comparing the diagram from my Marvel booklet It appeared that the venturi block had been previously placed in upside down with the long taper on the top instead of the bottom. Also the idle jet was 1/8 higher than the block. The diagram shows the jet below of the short taper end. Also the dashpot valve shows the sharp edge centered to the block . Apparently the last person to work on it found that the swollen di-cast venturi and dashpot fit better with it's edge on top of the block.

post-79073-143142299127_thumb.jpgThe photo shows the poor fit when I flipped the venturi block to the correct as indicated by the in the diagram position. I spent several hours carefully filing and fitting both the venturi block and dashpot valve to the carb bore.

post-79073-143142299249_thumb.jpgThe idle jet now is just slightly lower than the top of the venturi but not as low as in the diagram.

post-79073-143142299336_thumb.jpgI also scribed a line in the float bowl 1/8" lower than the height of the idle jet to adjust the float to maintain the fuel level according to that line. The old level was 3/8" higher as indicated by the ring around the bowl. I made a new carb to heat riser gasket from rubber/ fiber 1/16" Felpro material purchased from NAPA. Eliminating the heat slot. This is instead of the copper asbestos type since I have eliminated all heat access to the riser. I took "Beulah" out for a drive yesterday (35 degrees) and she preformed much better although she was sluggish in 3rd gear. More tweaking!

Larry

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Larry, I found the same with the air valve / flap in my 25 master. Not closing properly and a gap, mine was also sticking in the open position. So as you said, lots of filing and adjusting to get a proper fit. The engine did run better, but there is also an over heating problem, so I could,t run the engine for long before it over heated. Since I,ve been working on the body and other car projects, I haven,t got back to the over heating problem. My wife is over seas for a month, I promised her I would work on the house but I guess it would,t hurt to have a look at the water pump and flush the radiator out.

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Rod:

Interesting that since I have had the car, the adjuster spring for the dashpot never did anything no mater what position it was in. With the venturi block and the dashpot valve refitted, now I can adjust engine speed with it and clean up the idle. Just like the service manual states! I went out today to check and the carb was still leaking from the air horn so I bent the float arm lower still.

Started up and ran for about 20 minutes. Seemed to run well. I will check again tomorrow.

Larry

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Larry,

Great to see the progress. I had the same issues with my carb and had to go through and file down the venturi block and and the bottom edge of the dashpot valve too. It's part of the process I guess.

Dave

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After the run last night and shut down all seemed well. I talked to Terry Weigand about the Stewart Vacuum tanks operation. Noting that once I had a good smooth idle I would hear a faint pressure release from the tank every so often as it cycled. There was no noticeable change in engine RPM at that moment of cycling.

Checked today and there was still a puddle on the splash pan. GIRRRRRR!

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Larry,

I always close the fuel shut off valve between the vacuum tank and the carburetor when I park the car for more than an hour. The metal seated float valve will weep unless it is perfectly seated. Needle valves tend to rattle in their seats with the engine vibration and will eventually weep. To fix this, you can re-grind the needle and seat with very fine valve grinding compound or tooth paste.

Most production needle valves have "coined" seats. This is done by firmly hitting the needle into it's seat to create a perfectly mated needle and seat. But I don't recommend doing this to an antique carburetor....

Edited by Mark Shaw (see edit history)
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Mark! Mark! you scare the crap out of me with this whacking on things with hammers. I think you have been hanging around Brother Brian too much these days. To get serious though, I think you have something there with the needle and seat leaking. This is why replacing a seat with Viton (sp) seems to help the leaking problem. I have been in the habit of closing the fuel valve on the bottom of the vacuum tank after shutting the engine off for as long as I can remember. I was told that the pressure of the fuel would cause the needle and seat to leak or 'weep' as you say if the seat was not in the best of condition. I talked with Larry last evening and I told him that I was sending him a copy of the Stewart Vacuum Gasoline System Instruction Book. This little brochure talks about some of the very same problems that he is having and what they recommend to do. It will be interesting to hear what he has to say after looking this over. I told him again last night that it is just going to take some time to get everything sorted out. When he does he is going to have a sweet running engine.

Terry Wiegand

A VERY COLD Doo Dah

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I agree with Mark. I have to turn off my valve between the SW vac. tank and the carb. for parking greater than an hour or the whole SW vac. tank volume of fuel will end up leaking out of the carb and into the catch tray Buick designed to catch these leaks. Could I fix this with a viton seal on the carb. float needle? Sure, if I had a viton needle the correct size, etc..

The good news is, when you open the valve for the next start, there's plenty of fuel still in the SW vac. tank to feed the carb. and not make you crank and crank to get fuel back up to the engine.

I've enjoyed the carburetor discussions. I'm currently working on a 1960 CJ5 Willys and the little Carter Carb. on it. Just rebuilt it. What I found inside was really a mess, last guy must have rebuilt it with an axe and a rock. Everything bent or in backwards if they could force it. Now it purrs.

And Brother Doo Dah, I would only 'coin' you. I'd say $0.25 worth from a 5# sledge would get your attention.:cool:

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LOL... 25 cents worth from a 5 pound sledge...Thththththththth...

My old 15 will drip for a bit when I first shut it off from fuel that is already in the manifold and carb intake. It is just the nature of the beast. I shut the valve off as others do also and the car can sit all winter and still have gas in it come spring. If I need to prime it, there is something wrong. Dandy Dave!

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  • 2 weeks later...

You might want to consider removing that fuel filter. Most fuel filters require more pressure than gravity will provide and usually lead to sluggish performance at higher speeds, (as you say you have). Also, the gas is taken from the high part of the vacuum tank funnel shaped bottom, allowing the crud to settle down in the middle where it can be occasionally run off.

If you MUST use a filter, put it between the gas tank and the vacuum tank. You should have more suction working for you there.

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I might add, I have no idea if the carb on my 24 drips or not since I shut off the gas after every stop. Just safer that way, leaks or no leaks.

Consider also what Dave says above about gas running back from the manifold after shut off. Several of my updraft carb type cars do this.

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Jerry and Dave:

Thanks for the thoughts. Seems to have dissipated so the what may have been in the riser and manifold is done. I also think since it has been cold what does drip does not evaporate as readily as at 90 degrees.

Here in Pa. it may be close to 60 degrees this weekend so we may take Beulah out for a spin and check again.

Larry

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  • 3 weeks later...

What do you guys think about a micro switch with a float in the vacuum tank to work with an inline 4psi pump? The float could be set to fill the cannister about 3/4 full and would gravity flow to the carb.I found a site that had Stewart vacuum tops for sale without the internals.That way I wouldn't have to modify my original top.

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There is more than one way to skin a cat. As long as you are filling the vacuum tank, and letting only the weight of the fuel in the vacuum tank fill the carburetor, it should work. To do this the top of the tank must remain vented, and the switch set to turn on and off with float. Of course you are taking a proven system that works as is, and complicating it. The more stuff you add, the more that can go wrong. Dandy Dave!

Edited by Dandy Dave (see edit history)
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There was a guy that that had a 25 buicik in the Bugal that featured the 25's that was giving him a lot of problems if he drove the car more than 2 or 3 miles at a time.He said he made a look a like cannister and put a float and micro switch and electic pump and was able to drive the car anywhere he wanted to go.My 25 is having the same problem it will not keep enough fuel in the cannister.I want to be able to enjoy this car and drive it anywhere i want to go.The switch will be covered and not be that notisable.

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Since 1970 I have ben driving my 1925 Buick model 25 and never had any problem with the fuel canister,can`t understand why it needs to be an electric fuel pump on this type of vacum pump canister.

I have almost the same type on my 1923 and 1924 Buick 4 cyl.models and never had any problems.

Be sure there are no leak in the tube from the fuel tank to the canister,and clean the canister.As well as no leak from the engine vacuum tube to the canister.

Leif in Sweden.

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Before I jump into the electric pump deal I think I will get the carb overhauled and try the cannister one more time.I have already cleaned the cannister out and installed a new kit from Bobs Autobillia which consist mostly of springs and gaskets.My problems all started with Ethanol and am now using non Ethanol fuel.I would rather keep the car original.I have owned the car 10 years now and have never had it running right.

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Micro cracks can cause loss of vacuum that will slow the refilling process and cause intermittent loss of power. Make sure the sealing surfaces are flat, and coat the under side of the top with Krazy glue (not affected by alcohol or gasoline) to seal the porous pot metal. Use a new gasket and flexible gasket sealant to make sure you have no leaks.

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I have had a number of 1920's cars over many years all with vacuum tanks. Each car has been driven many miles . Vacuum tanks are extremely simple and reliable devices and there is absolutely no reason to modify them. However the pot metal tops can cause a problem and I always replace them with a reproduction top. The originals can crack or warp and leak. The internal seats for the 2 valves have small brass inserts in the top and they can come loose and fail to shut off when the pot metal expands around the insert. The reproduction tops in aluminum or brass do not have or need these inserts.

I have experienced vapor lock where the vacuum tank is located over the exhaust manifold . In this location the fuel is preheated and in hot weather this can lead to vapor lock. Many solutions to this problem have been exhaustively discussed on this forum over the years.

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Don't know if any of you have seen one so I am attaching a Marvel calibration chart with the first 2 entries applying to our cars. Float height to be 9/16" measured from the top of the bowl. I bought the booklet "How to Overhaul a Marvel Carbureter", From "BOBS" and the same chart was in it. Also a Mason-Dixon Buick club member who just bought a 1931 96S Sport Coupe', sent me a copy of an original. He received much original paperwork with the Buick Engineering Department Stamp on it! The Marvel book I bought has some good tips and some illustrations dealing with Marvels up to 1932. I tried to start my car the week before the cold set in so I could circulate the added anti freeze. It was only good to +15 degrees. First it flooded badly then was starving ??? Today it was 55 degrees here so I thought I would try again. I used the electric pump to prime the vacuum tank until I heard the tank float flip. Started right up and quickly died like it was starving. Did this several times. I noticed that there was no fuel flowing into the fuel filter below the Vacuum tank. I disconnected the fuel line below the tank shut off valve. Barely a trickle at full open. So I removed the valve, disassembled and found a blockage. A small glob of RTV blue sealer that probably came from when I sealed the top of the tank. I drained the vacuum tank to check for any other debris. Reinstalled all, started her right up! Could now watch the fuel now flowing thru the filter andhear the tank cycling. Ran her for a half hour till warm. Tomorrow may try for another ride.post-79073-143142346818_thumb.png

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Be advised that RTV silicone will not stand up to gas. It will swell up and crumble into pieces. The top of these vacuum tanks should not need sealant of any kind as the gaskets are thick enough to accommodate slight irregularities. Get that silicone out of there as leaving it will just cause more problems!

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  • 2 weeks later...

Started up Beulah last Tuesday since we had another snow day! Our 4th, the summer is getting shorter for me. Also started Lucy the 1937. Still a bitter cold day. High around 20 degrees. Had to play with the choke after she started to run to keep her running but after a minute she smoothed out with the choke pushed in. Ran both cars for about a half an hour and both seemed very happy. Tonight I will put the warming glow of 100 watt incandescent bulbs around the engines. It is to go below 0. I had drained the radiators and refilled with fresh antifreeze. There was already a 50/50 mix. But even with the higher concentration my tester says things are only good for +10 degrees.

Burrrrr

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  • 2 months later...

Update on the vacuum tank.

Over the weekend we put about 10 miles on each of our Buicks. Took the 1937 out on Saturday and the 1925 on Sunday. The 25 ran Ok but still not quite up to how it should run. Each carb adjustment seemed to secure a bit more power. Vacuum tank seems to be working fine. After shut down and shutting off the fuel valve at the vacuum tank I put a small coffee under the carb. I expect a bit falling from the riser. But after several days I have over 1/2 pint collected. So it has to be backing up from the Vacuum tank into the manifold. I have seen some setups that the vacuum line has a loop in-between the tank and the manifold would this have an effect?

Still dripping!!!!!

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