Morgan Wright Posted September 16 Share Posted September 16 (edited) Definitely true! And I have proof: Recently I parked my car at a car show, and shut off the valve at the bottom of the vacuum tank, to prevent any dripping that might happen. After the show, I forgot to open the valve, and started the car and drove around the place, after a minute the car started sputtering and running bad. I did everything I could think of to make it run better, rev the engine, let it warm up, adjust the choke, timing advance lever, idle mixture screw. Nothing would make it stop sputtering and running rough, making black smoke. After 5 or 10 minutes of running rough, I noticed the vacuum tank valve was shut off!! I opened the valve and about 5 seconds later it started running normally again! So, for 5 or 10 minutes, the carb bowl was empty and the fuel was bypassing the carburetor and going directly into the intake manifold!!!! Ha ha now I know it's true. . . Edited September 16 by Morgan Wright (see edit history) Link to comment Share on other sites More sharing options...
Leif Holmberg Posted September 16 Share Posted September 16 The same has happend to me a couple of times and the problem are the vacum tanks needles or nozzle.Open upp the top of the vacum tank and see if the needle or nozzle are in right place! The same can happend even if the valve below the tank are open but it`s a lot harder to understand what happends when fuel goes both thru the vacum tube as well as thru the carburetor! Link to comment Share on other sites More sharing options...
garnetkid Posted September 16 Share Posted September 16 Had that happen as well years ago..running very rich..I even turned the manifold over and put a down draft on it until I found the problem.. 1 Link to comment Share on other sites More sharing options...
nat Posted September 16 Share Posted September 16 52 minutes ago, garnetkid said: .I even turned the manifold over and put a down draft on it Clever. Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 16 Author Share Posted September 16 5 hours ago, Leif Holmberg said: The same has happend to me a couple of times and the problem are the vacum tanks needles or nozzle.Open upp the top of the vacum tank and see if the needle or nozzle are in right place! The same can happend even if the valve below the tank are open but it`s a lot harder to understand what happends when fuel goes both thru the vacum tube as well as thru the carburetor! I think my only problem is I forgot to open the valve at the bottom of the vacuum tank. Link to comment Share on other sites More sharing options...
old car fan Posted September 16 Share Posted September 16 Can't happen unless there's a problem. 2 Link to comment Share on other sites More sharing options...
nat Posted September 16 Share Posted September 16 23 minutes ago, Morgan Wright said: I think my only problem is I forgot to open the valve at the bottom of the vacuum tank. When the vacuum tank is full, the float should shut off the vacuum to fuel tank connection and open the tank to atmosphere valve. One or both of those would have to be out of order if the engne runs/floods with the petcock closed. 1 Link to comment Share on other sites More sharing options...
old car fan Posted September 16 Share Posted September 16 To add to that, vacuum tank is never full,as full as the bottom of the float, again if its full, another problem. Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 16 Author Share Posted September 16 2 hours ago, nat said: When the vacuum tank is full, the float should shut off the vacuum to fuel tank connection and open the tank to atmosphere valve. One or both of those would have to be out of order if the engne runs/floods with the petcock closed. What if the vacuum tank was in the refilling mode when I turned the engine off and shut off the valve? Then, the manifold valve would be open, and when I restarted the car there would be enough fuel in the carb to get the car running for a minute and then it would just suck all the fuel coming in the fuel line, right into the manifold, and it would never get full enough to raise the float and shut off the manifold valve. The inlet for the fuel line from the gas tank is right next to the valves for vacuum tank. Fuel would all just shoot in and none would go to fill the vacuum tank. Link to comment Share on other sites More sharing options...
nat Posted September 16 Share Posted September 16 3 minutes ago, Morgan Wright said: then it would just suck all the fuel coming in the fuel line, right into the manifold No because the atmosphere vent should open before the tank, (overfills), and overflows into the manifold. 1 Link to comment Share on other sites More sharing options...
Leif Holmberg Posted September 17 Share Posted September 17 Here is the nozzle that caused the problem on my 1924 4 cyl. A similar problem has happend on my 1925 6 cyl.as well but can`t find any photos. Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 17 Author Share Posted September 17 16 hours ago, nat said: No because the atmosphere vent should open before the tank, (overfills), and overflows into the manifold. My theory is not that it overflows into the manifold, it's being SUCKED into the manifold directly from the fuel line at the top, when the float is down and the manifold valve is open and the atmosphere valve is closed. Link to comment Share on other sites More sharing options...
nat Posted September 17 Share Posted September 17 47 minutes ago, Morgan Wright said: My theory is not that it overflows into the manifold, it's being SUCKED into the manifold directly from the fuel line at the top, when the float is down and the manifold valve is open and the atmosphere valve is closed. Yes, it does get sucked in which can only happen if it's overfilled. Link to comment Share on other sites More sharing options...
Terry Wiegand Posted September 17 Share Posted September 17 You guys might remember my posting about the problem that I had with the lid (cover) on the vacuum tank on our D-45. The problem was the swelling of the forks in the lid that holds the float mechanism and the needle for the vacuum shutoff. The problem was that the tank would fill like it should and the float stuck in that position. This shut off fuel from being pulled from the gas tank. The engine would use up what fuel was in the tank and then starve for more fuel. The motion and jostling around with the car going down the road would then knock the float loose and things would go back to operating as they should. The point that I am trying to make is that if the vacuum is shut off going into the tank it is almost impossible for the engine to suck raw gas into the manifold above the carburetor. The only reason that I can see for fuel being sucked into the manifold with a full vacuum tank is because the needle is not seating into the seat in the lid properly. Back in the day these systems were very reliable so long as everything was maintained properly. If the fuel shutoff on the bottom of the vacuum tank is left closed the engine will run for a bit until what is in the float bowl is gone. Terry Wiegand South Hutchinson, Kansas AACA Life Member #947918 1 Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 17 Author Share Posted September 17 (edited) 2 hours ago, nat said: Yes, it does get sucked in which can only happen if it's overfilled. That's not what I'm saying at all. I'm saying it gets sucked in from the fuel line inlet which is only 1/2 inch away. Fuel from the gas tank comes in at the top lid of the vacuum tank, as it falls and splashes around some of it gets sucked into the manifold. Some of it falls into the upper compartment and raises the float and shuts off the manifold valve but who knows how much and how long it would take? Edited September 17 by Morgan Wright (see edit history) Link to comment Share on other sites More sharing options...
Hubert_25-25 Posted September 17 Share Posted September 17 You have to look very closely at this photograph. I have added another enlarged photo. This is the correct set up for a 1925 Buick. There is a screw in brass fitting into the aluminum lid for the vacuum line. I do not know what size hole this is, but it is smaller than 1/16". Maybe the size of a wire brush bristle. This may or may not be installed on your vacuum tank. That tiny hole is not going to feed much gas. Maybe this is missing? Was this tiny hole a safety feature to prevent a backfire issue in the vacuum tank? This hole and vacuum source is on the top of the vacuum tank. So the tank would have to be liquid full, or the car can idle while running off the vapor space fumes. If the tank were liquid full, then the float would cause the vent to be open so maybe it can sustain an idle while the tank is not full? I will get fuel fumes in my house if the car in my shop has a hint of too much gas. Before leaving a car in the shop, I leave the doors and a window open. I close the valve under the vacuum tank and I let the engine idle to run the gas out of the float bowl. The car will die in about a minute. So no, my car will not do as you suggest. Hugh Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 17 Author Share Posted September 17 (edited) 22 minutes ago, Hubert_25-25 said: I close the valve under the vacuum tank and I let the engine idle to run the gas out of the float bowl. The car will die in about a minute. So no, my car will not do as you suggest. Hugh Back when I had a fuel filter with a glass bowl in the fuel line, I could look at the gasoline coming in and could see the operation of the vacuum tank by watching the gasoline, when the engine was idling. When the vacuum tank was filling, the fuel would swirl around the glass bowl of the filter like crazy for about 15 seconds, and then stop. During the emptying process, it took about 2 full minutes to empty. So the vacuum tank takes 15 seconds to fill and 120 seconds to empty. If you shut your car off during the 120 seconds, the manifold valve will be closed and the engine would die when the carb bowl was empty. But what if you shut your car off during the 15 seconds? The manifold valve would be open. I can see why they designed the vacuum tank with a 1 inch nozzle on the fuel inlet, to prevent gas from splashing into the manifold. See here: Edited September 17 by Morgan Wright (see edit history) Link to comment Share on other sites More sharing options...
nat Posted September 17 Share Posted September 17 The only vacuum tank I've dealt with is on my 24' Dodge which will run out of fuel in about 30 seconds if fuel to the carburetor is shut off. This description and diagram is for the Dodge. The parts would be different than Buick but they both operate in the same manner. Link to comment Share on other sites More sharing options...
Oldtech Posted September 18 Share Posted September 18 Usually... if they suddenly start doing this it is because the float has sprung a leak and sunk. The orifice shown in Hubert's picture is s'posed to limit the amount of fuel it will actually suck. If it is missing it will all work fine until there is a float or other overfill issue. I've never heard of them "splashing over". 2 Link to comment Share on other sites More sharing options...
nat Posted September 18 Share Posted September 18 12 hours ago, Oldtech said: Usually... if they suddenly start doing this it is because the float has sprung a leak and sunk. That fits since the float level should shut the fuel valve and open the atmosphere valve, either one of which should stop the tank from filling. Link to comment Share on other sites More sharing options...
nat Posted September 18 Share Posted September 18 (edited) Have you checked your float and upper chamber for leaks? I think Oldtech zeroed in on your problem. Edited September 18 by nat . (see edit history) Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 19 Author Share Posted September 19 Interesting. That pinhole was for my spare vacuum tank. I just measured the one in the vacuum tank currently on my car and it's much bigger, fits a #55 jet drill bit which is 0.052", twice the size of the other. I wonder if they reduced the size of the hole to address this problem. Maybe I'll swap 'em out and see what happens. 1 Link to comment Share on other sites More sharing options...
nat Posted September 19 Share Posted September 19 2 hours ago, Morgan Wright said: I just measured the one in the vacuum tank currently on my car and it's much bigger, fits a #55 jet drill bit which is 0.052", twice the size of the other. Doubling a diameter quadruples the area. Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 19 Author Share Posted September 19 34 minutes ago, nat said: Doubling a diameter quadruples the area. Ain't it the truth!! Anyway, I swapped out the one with the quadruple hole for the one with the small hole and the car still runs great, I just drove it for 4 miles with the small hole. We'll see. 1 Link to comment Share on other sites More sharing options...
Morgan Wright Posted September 20 Author Share Posted September 20 (edited) Today I took the lid off my vacuum tank to make sure. Guess what. Once every 30 times of clicking the manifold valve, it gets stuck. Time to replace it with the spare one. Job done, and now it runs fine with the new lid (I didn't replace the whole tank, just the lid with the float and everything attached to it). So: Edited September 20 by Morgan Wright (see edit history) Link to comment Share on other sites More sharing options...
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