Guest Merchant Xpress Posted February 2, 2009 Share Posted February 2, 2009 I have a vacuum fuel supply tank on my 29 DB pickup, and a new Zenith Carb. The truck starts and runs but I've noticed the inline fuel filter between the vacuum tank and carb seems to be cavitating badly and the carb runs out of fuel after running a couple of minutes. The carb will refill after the engine stops and start right up and run again until it runs out of fuel. I'm not sure what is going on here and can use suggestions on what anyone thinks may be going on here. By cavitating I mean lots of bubbles entering the filter so it looks as though the fuel is boiling.Harry Link to comment Share on other sites More sharing options...
keiser31 Posted February 2, 2009 Share Posted February 2, 2009 Is the fuel boiling? Is it a metal fuel line? Is the fuel line too close to a heat source? Maybe the inline fuel filter is plugged somewhere near the inlet. Link to comment Share on other sites More sharing options...
keiser31 Posted February 2, 2009 Share Posted February 2, 2009 Have you tried running the truck without the inline filter to see if the fuel still bubbles and carburetor still runs out of fuel? Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 2, 2009 Share Posted February 2, 2009 John, not boiling from heat. I don't think the filter is obstructed as I think that would only cause the filter not to drain, I don't think I would see the boiling action. Like I said it isn't truly boiling it just looks that way from all the air bubbles.Harry Link to comment Share on other sites More sharing options...
Steve Braverman Posted February 2, 2009 Share Posted February 2, 2009 Try putting the filter before the vacuum tank. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 2, 2009 Share Posted February 2, 2009 Steve, I'll try that. I'm wondering if the vacuum is pulling fuel back from the carb causing the turbulence in the filter? If the flapper valve isn't closing tightly I might be getting a reverse flow back into the filter. That might explain things.Harry Link to comment Share on other sites More sharing options...
Guest Fr Mike Posted February 2, 2009 Share Posted February 2, 2009 Hi Merchant Express!For whatever it may be worth, I had a mystery situation very much like yours, after acquiring my 1931 Buick. Rebuilding the fuel pump and the carburator, checking for air-tightness of the seating of the clean-out bowl on the fuel pump, cleaning out and re-lining the gas tank, and blowing out the fuel line didn't resolve the problem. I even ran a wire through the fuel line. Still no help. Finally, I replaced the fuel line with a new one, and BINGO! Everything began to run smoothly the way it's supposed to. What had happened was that, over the years of use, the inside walls of the fuel line had become coated with deposits that had hardened and had reduced the inside diameter of the line. As a result, the gas supply was too slow to keep up, and the carburetor became starved except when in idle mode.Hopefully, sharing this may be of value to somebody.Good luck! Link to comment Share on other sites More sharing options...
jan arnett (2) Posted February 2, 2009 Share Posted February 2, 2009 Sounds like you are getting air into the line between the vac tank and carb. Take the fittings off and use some teflon tape on the fitting, around the line where it goes into the tank and see if it helps.Jan Link to comment Share on other sites More sharing options...
carbking Posted February 2, 2009 Share Posted February 2, 2009 Where did you acquire the Zenith carb? They have to be modified to use a vacuum tank.Jon. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 2, 2009 Share Posted February 2, 2009 Jon, I got the carb directly from Zenith, I will call them and find out what has to be done. Or I will put the electric pump on and sell the vacuum tank. Either way can work for me.Harry Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 2, 2009 Share Posted February 2, 2009 Fr Mike, thank you, I have new lines from the vacuum tank to the carb so I don't think the line is the problem.Jan, I will check all the hose clamps for tightness, maybe something is sucking air.Jon, since the vacuum tank should just be supplying gravity feed why would that cause a problem? Unless the flapper valve is letting fuel suck back from the carb. I know an electric pump will supply more positive pressure and that may be the answer. Would I need to add an anti percolation valve if I stay with the vacuum tank?Harry Link to comment Share on other sites More sharing options...
Guest rbl2 Posted February 3, 2009 Share Posted February 3, 2009 My 26 Chevy uses the same system as your car. I have two fuel filters on it. A modern one, clear plastic so I can see how dirty it is, is placed about 18" from the gas tank where it can't be seen w/o some effort. I also have a sediment bowl/filter just about 2" from the vacuum tank on the gas tank side. With the engine idling I can watch it "bubble" very briefly, less than a second, about once a minute or two. That happens when the vacuum tank refills as it is supposed to. At an increased idle speed the bubbling cannot be seen as it refills much more quickly. My car runs fine. However. for a long time it used to run for about 7 minutes and quit. I actually timed it. It would start right back up and do it again. I replaced everything no less than twice and many things 3 times. There's not that much there that can cause problems.After much grief I concluded the problem was in the vacuum tank even though I had replaced it 3 times with rebuilt ones. A gentleman whom I have never met on the other side of the continent took the vacuum tank off his running 28 Chevy and gave it to me, gave as in free, just to see if that would solve the problem. It did. Three years later I'm still trying to figure out how to repay that mans kindness. I also had a problem with crud in the gas tank. The tank had rusted and by the time I caught it, it was too late. Long story short I had it cooked and lined. I kept a close eye on the sediment bowl and carb for several hundred miles after that. There was a very fine substance that would get past both fuel filters and into the carb. I could drop the carb bowl and see what looked like a very small am't of fine dust in it. That "dust" would clog the carb. It was easily washed out with B12 and blown away with light air pressure. An electric fuel pump would cause more problems then it would solve. They put out too much pressure for those old carbs. I do know of one man who uses one when he needs to go up long hills. The load on the engine robs it of using vacuum for the tank, much like it would for vacuum windshield wipers. He has a toggle switch on it and turns it on for just a second or two as needed to refill the vac tank. I have found that when there is a problem with vacuum tanks it's usually in the vacuum line or inside the tank itself. One time I found one that the flapper valve wasn't closing correctly. The car would run but would sometimes stop as if it was out of gas. The pot metal holding the flapper valve clip had a hairline fracture in it. The inner tank had to be replaced to solve the problem. Make sure all your fittings are tight. No need for teflon. Mine doesn't have any on it. It wasn't used in the day. I'm told it can cause problems but I don't see how if it is applied properly. If you use it, make sure none is covering the opening in the fuel or vacuum lines. Inside the tank, where the float attaches to the top, are some very small openings. That's where my problem was. Those little openings were clogged and it was very difficult to see. I found it only by comparing one with another. A good soaking of B12 and a paper clip solved that problem. Also make sure the float is good and does not have fuel in it. You can hold it close to your ear and shake it, listening for gas sloshing around in it. You can also place it in a pot of very hot water and look for air bubbles.You don't need to add anything to your fuel system such as an anti-perc valve. It wasn't needed years ago and it's not needed now. Those cars ran just fine the way they were made. I drive mine all the time. It does fine around town as well as on the open road, although I only drive it at about 45 mph.I hope I have been of some help to you. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 3, 2009 Share Posted February 3, 2009 Bill, lots of good information. I think the vacuum tank is probably the problem but I'm not sure it is worth messing with. My carb is a brand new Zenith so I'm pretty sure it will stand up to the electric pump pressure, especially if I put a pressure regulator in line. I will try the pump anyway just to see if it cures the dieing problem.Harry Link to comment Share on other sites More sharing options...
Steve Braverman Posted February 3, 2009 Share Posted February 3, 2009 Vacuum tanks are simple and reliable. Electric fuel pumps are the work of the devil. Link to comment Share on other sites More sharing options...
JohnD1956 Posted February 4, 2009 Share Posted February 4, 2009 Having never owned a vehicle this old, can someone educate me on how the vacuum tank works for supplying fuel? I'm just curious, that's all.Thanks Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 4, 2009 Share Posted February 4, 2009 John, I'll tell you how it works on the DB truck. The oil pump is also a vacuum pump that hooks to the top of the vacuum tank. The tank is actually two tanks. The external tank is a storage tank for excess fuel. The internal tank has a float that is connected to a couple of valve assemblies in the top and the bottom of the internal tank has a flapper valve on it. When the float is down the vacuum valve opens and pulls the flapper valved closed, the vacuum pulls on the fuel line sucking gas into the tank, when the tank fills the float trips the vacuum valve shutting off the fuel flow and opens a valve to atmosphere so the gas can drain to the carb. The reason DB hooked to oil pump was is you lost oil pressure you also lost vacuum and the fuel would shut off before you burned up the engine.Anyway, the vacuum tank should work as long as all the surfaces are tight and the valves and float are working correctly. Something in mine isn't working correctly.Harry Link to comment Share on other sites More sharing options...
Guest rbl2 Posted February 4, 2009 Share Posted February 4, 2009 If I had one if front of us I could explain it much easier. I'll do the best I can. They are a remarkably simple device and quite reliable, albeit with a few shortcomings. I read someplace the technology behind these things is about 3,000 years old and still used in jet engines. Don't quote me on that. The vacuum tank is a cylindrical shaped object with a seperate canister inside it that is about 2/3 the length of the outside canister and rests on the top of the outside canister. With me? Think oatmeal box with an inner canister.At the bottom of that inner canister is what is called a flapper valve. More on it later but that's all there is to the inner canister.The top of the vacuum tank has 3 lines running to it. One is supply (fuel), another is vacuum, and some, but not all, have a third, which is for overflow. Attached to the top, on the inside, are 2 small wires that go through a tube to where the vacuum line is attached. One is an atmospheric valve and the other a suction valve. It is important that these wires are clean and move freely. B12 will do a good job of cleaning them. There is a small gap of about .018-.028. No where have I ever seen how to make this adjustment. These wires attach to a float. On the bottom of the outside canister is the line that feeds gas to the carb. When the canister is low on fuel the float drops, opening the vacuum valve. This then pulls fuel from the gas tank. The vacuum also shuts the flapper valve, which stops the fuel from the inner cannister from flowing to the bottom of the outer canister. Still with me? Once the inner canister is full the vacuum is shut off. The flapper valve opens and fuel from the inner canister drops to the lower portion of the vacuum tank where it is gravity fed to the carb. There is an adjustment on the flapper valve of .022 -,028 but I have never figured out how to adjust it. I do know if it's not opening enough gas will not flow freely to the lower portion of the canister thus causing the carb to run low on fuel. If it opens too much the inner tank will never fill with fuel and the carb will flood. Make sure the flapper valve and the area where it seats is clean, free of any lint and abrasions as these could cause it to not shut completely.The process then repeats itself as necessary. Under load the vacuum tank does not receive enough vacuum to pull gas from the tank.Remember vacuum windshield wipers that wouldn't work when going up hill or in 1st or 2nd gear? Same thing with the vacuum tank. I've only had the vacumm tank low on fuel once going up a hill. I simply took my foot off the gas pedal for 1 or 2 seconds and all was well again. It's my understanding the fuel in those tanks is good for about 7 miles. A simple test of the vacuum tank is to remove the inside, fill the canister with gas, and see how the car runs that way. If it runs ok then the problem is not in the carb or in electrical system.Having done that you can set a gas can on the running board and run a clear line (avaliable at most hardware stores) from it to the vacuum tank. Being clear will allow you to watch as it pulls fuel. Once the vacuum tank is filled the fuel in the hose will drop back to the gas tank. This is my back up computer, If I had my regular one, which is under repair, I could post pictures and links that would clearl;y show the insides of a vacuum tank making it much easier to understand what I've been talking about. No doubt I have made a very simple process and piece of equipment sound very complicated. My apologies. More simply, the vacuum tank pulls fuel from the gas tank. When the vacuum tank is full it quits using vacuum, the flapper valve opens allowing gas to gravity feed to the carb. Once the float reaches a certain level the vacuum valve opens, pulling the flapper valve closed and pulling gas from the fuel tank. Which reminds me. Make sure the fuel line from the bottom of the vacuum tank to the carb is on a downhill slope. Otherwise the carb may starve for fuel. I hope this helps. Link to comment Share on other sites More sharing options...
Guest rbl2 Posted February 4, 2009 Share Posted February 4, 2009 While you were writing you much more simplified and understandable description of vacuum tanks I was typing my much more complicated and not understandable description with two fingers. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 4, 2009 Share Posted February 4, 2009 Bill, mine was probably too simplified and I'm sure there are some fine points I didn't cover. I think I'm going to put on the electric pump, (sorry Steve) while I have the vacuum tank rebuilt by someone who knows what they are doing. I hope I don't have to send it to Australia to get it done right.Harry Link to comment Share on other sites More sharing options...
Guest rbl2 Posted February 4, 2009 Share Posted February 4, 2009 There are people in the states who rebuild them. I got mine from Gary Wallace. He deals in Chevy 4's (pre 1928) I don't have a link to his website but here's his ph no. I don't doubt at all that he can help you with your vacuum tank314-293-1991He owns cars other than Chevys and no doubt ois familiar with them. As well, there weren't too many manufacturers of vacuum tanks. I have enough spare parts to build another one or two. I may do that when it warms up. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 4, 2009 Share Posted February 4, 2009 Bill, thank you, I will call Gary and talk with him.Harry Link to comment Share on other sites More sharing options...
JohnD1956 Posted February 5, 2009 Share Posted February 5, 2009 Thanks for answering that question. I always enjoy learning new stuff about old cars. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 5, 2009 Share Posted February 5, 2009 John, talk about learning, I just spent half the day messing with a Stewart Warner 6 volt fuel pump trying to figure out why it isn't pumping. I won't tell you how many times I took it apart and put it back together before I realized there isn't a diaphragm in the stupid thing. I bought it a few years ago but never needed it so had never checked it. Boy, did someone see this sucker coming! I feel like such a dope, not only for not checking it as soon as I received it but also for taking it apart so many times before I realized what was missing, DUH.Harry Link to comment Share on other sites More sharing options...
Steve Braverman Posted February 5, 2009 Share Posted February 5, 2009 All the time you spent messing with the evil electric fuel pump, you could have cleaned out your vacuum tank and had the truck running again. Usually a good cleaning is all they need. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 5, 2009 Share Posted February 5, 2009 Steve, I completely took it apart and cleaned everything inside and out including the wires and the flapper and matching surface, the tank isn't pulling. I will send it to someone who is willing to take on the task and hook up an electric until I get it back. Do you know of anyone who is willing to work on a vacuum pump?Harry Link to comment Share on other sites More sharing options...
Steve Braverman Posted February 5, 2009 Share Posted February 5, 2009 The tank is such a simple device. Are you sure it's getting vacuum? It the float moving up and down? Did you fill the tank to prime it? A vacuum tank must be filled manually before it will work. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 5, 2009 Share Posted February 5, 2009 Steve, I did fill it to prime it, it is getting vacuum but somewhere in the process it doesn't keep filling, the truck runs until all the prime is gone then I have to start all over again. While that is all happening the other condition is happening with the fuel bubbling in the filter. It's almost like the fuel is pulling back from the carb. The carb doctor said my carb needs to be modified but he didn't say how. That being his business I don't expect him to give away free information, I'm sure Zenith knows what needs to be done. Still the vacuum tank, I think I'll make a new top gasket to see there is a leak there, something isn't working right.Harry Link to comment Share on other sites More sharing options...
carbking Posted February 5, 2009 Share Posted February 5, 2009 If you install the electric pump, you will probably find the carburetor quits "running out of gas". Then when you reinstall the vacuum tank, it will start running out of gas again.Jon. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 5, 2009 Share Posted February 5, 2009 Jon, why is that? Is there not enough pressure with the gravity flow?Harry Link to comment Share on other sites More sharing options...
F&J Posted February 5, 2009 Share Posted February 5, 2009 If it were me; I'd put a vacuum gauge on the vacuum tank to see if that crazy setup off the oil pump is working Ok. If it's not making enough vacuum, I'd run manifold vacuum to the tank. Link to comment Share on other sites More sharing options...
Guest Merchant Xpress Posted February 6, 2009 Share Posted February 6, 2009 Yeah, I thought of that when I first started having problems so I hooked up to the manifold while I'm getting everything going. Just to make sure the oil vac pump wasn't causing the problem. The manifold vacuum is great so it isn't a lack of vacuum. For what it's worth the oil vac pump is pulling good vacuum also once I got the pump primed but until I get things worked out I'm going to stay on the manifold vacuum.Harry Link to comment Share on other sites More sharing options...
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