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Easy under dash fuel shut off from vacuum tank to carb


28Buick

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The guy who serviced the Marvel 30 years ago wrote the OO that Buick requires a fuel valve shut off whenever the engine is off for more than a few hours to prevent dreaded gasoline leaks. I have yet to find those words of wisdom in the manual, but it is good advice and is a PIA to pop the bonnet after each ride. Hugh pointed out that the Model A has an interior valve. So this inspired me to run the line from the vacuum tank through the steering column opening and back to the Marvel. I can now shut off the fuel while seated in the driver's seat and prevent gasoline overflow from the carb when the needle or float gets lazy. It is a quick fix as pictured here. I doubt it will be noticed at a show and the car smells much nicer.

 

fuel-petcock.jpg

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They make 6volt in line valves that open and close with the ignition switch. They work well.  

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     It's a good rig for ease of preventing fire but it won't go un-noticed on either side of the firewall.

     I'd gladly sacrifice car show points today if it increases the odds of having my car tomorrow.

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It won't work. When the car sits, that whole amount of gas in the line between your valve and the Marvel has to drip out through the carb, and it will be replaced with air in the line below your valve. The bottom of the vacuum tank is lower than the dashboard, so when you open the valve to start the car the air in the line will rise up to the highest point in your line, and the fuel in the line between the vacuum tank and the air bubble won't have the force to move the bubble down to the carb. 

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Morgan….thanks for the help with the hard engine parts. The Buick went to its final home yesterday. The 87 year old owner was thrilled with his car. It was a fun project. Best part of the whole experience is I enjoyed the car enough that I would own one…….quite a surprise as I didn’t think it would be as drivable as it was.

 

 

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Posted (edited)
16 hours ago, Morgan Wright said:

It won't work. When the car sits, that whole amount of gas in the line between your valve and the Marvel has to drip out through the carb, and it will be replaced with air in the line below your valve. The bottom of the vacuum tank is lower than the dashboard, so when you open the valve to start the car the air in the line will rise up to the highest point in your line, and the fuel in the line between the vacuum tank and the air bubble won't have the force to move the bubble down to the carb. 

Thank you so much for this note. The fuel shut off works great. The bottom of my vacuum tank is above the valve. When the valve is closed there is no air in the line, nor can any enter. The theory that gas in the line will drip out is illogical: How much fluid drips from a 1/4 inch hose that is air-tight at one end? None that can be detected. There are no air bubbles in a closed system. In actual practice the Buick is now starting on first try after not running for several weeks.

Edited by 28Buick (see edit history)
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Ah, the Marvel Drip.  Why Buick even designed a catch trough and steel flex hose below the Marvel to catch the fuel and keep it off the hot exhaust take down pipe.  At least 1923s have that. 
 

The issue in my case was bad gaskets on the bottom of the Marvel. See the pics that are upside down from how it mounts in the car but you can see the bad gasket joints (2) and the banjo too.  Then I show it apart.
 

I have found over the years it takes about an hour of sitting hot before enough fuel has departed where I get extended cranking.  Now with things better sealed I can go all afternoon. Keeps you looking good at lunch and ice cream stops on tour where you hate to let the other guys see you raise the bonnet for any reason. 
 

The comment from Ed that he liked that Buick 6 he sold made me smile. 

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On my 1925 Master it was a case that the shut off valve was not sealing well.

 I got it to seal then the male compression fitting at the valve was causing the next leak. I had to adapt another fitting to match the (Dole fitting/Tube nut). It has a 1/2"X 20 thread.

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I made an internal and external 60 degree lap. Used with with some heavy rubbing compound the valve is now sealing. When I got the car the brass line from the main tank was already cut and it had one of the large plastic filters there. Also an outboard motor primer bulb that was hard as rock.

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 On my 1925 Standard I installed an in line 1/4 turn ball valve just behind the carb. I just could not keep it from overwhelming the needle valve. I would also like to work up an easier way of accessing it without having to raise the hood every time.

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Edited by dibarlaw
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I would not run a fuel line into the passenger compartment.  Although the Ford Model A (photo below) does have the gas tank, shut off valve, and fuel line in the passenger compartment, I would not call this a "best practice".     Better options are as Edinmass suggests, or purchasing a valve style where only the handle passes into the compartment.  Even this style gives pause to ensure that the valve stem packing could not eventually leak into the passenger space.   Ford also used copper tubing which again is an upgrade to rubber tubing. 

 

This is a nice under dash photo showing the fuel valve in a Model A and some additional electrical splices in the near vacinity.     

 

On my Buick, when I am done for the day.

    - Park the car running.

    - open the hood

     - close the needle valve under the vacuum tank.  Note: my ignition is still "on" and I let the marvel run dry.  (About 2-3 minutes). Then I shut off the ignition. 

 

Another advantage of doing this is that if I do not drive the car for an extended period, the carburetor does not get gummy from fuel evaporating in it. 

 

Hugh 

 

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21 hours ago, 28Buick said:

Thank you so much for this note. The fuel shut off works great. The bottom of my vacuum tank is above the valve. When the valve is closed there is no air in the line, nor can any enter. The theory that gas in the line will drip out is illogical: How much fluid drips from a 1/4 inch hose that is air-tight at one end? None that can be detected. There are no air bubbles in a closed system. In actual practice the Buick is now starting on first try after not running for several weeks.

The whole purpose for the shut off valve is because the Marvels drip over time. Of course the line fills with air, it doesn't matter if one end is air-tight, the air gets in at the Marvel end to replace the drips.

 

But it's good that your shut off valve is lower than the vacuum tank, that means the air bubble rises up into the vacuum tank when you open the valve. If your petcock is lower than the vacuum tank and higher than the carb, it would work in a level garage.

 

 

.

Edited by Morgan Wright (see edit history)
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The carb on the 22 would hold fuel……..I rebuilt it but the float must be 90-100 years old cork. Was working fine and not falling apart, so I went with it. For such a bad reputation as the Marvels heavy, my only complaint is fuel milage on a small engine. Then again, tank is small also. And my foot seems to be heavy.

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4 hours ago, edinmass said:

The carb on the 22 would hold fuel……..I rebuilt it but the float must be 90-100 years old cork. Was working fine and not falling apart, so I went with it. For such a bad reputation as the Marvels heavy, my only complaint is fuel milage on a small engine. Then again, tank is small also. And my foot seems to be heavy.

Your heavy message is appreciated. As Emmett Brown asks, Why are things so heavy? Is there a problem with your gravitational pull? Anyhow somebody coated my cork float and the coating peeled and fouled the jets, so now it is a plastic float from Bob's that is guaranteed not to sink. Bobs list the float as a 1925 part but it works for all years. My Marvel no longer drips thanks to a well designed neoprene needle that was custom made by Hugh. That is a good idea to mount the fuel petcock on the firewall with the lever inside and all the lines on the engine side. I am reluctant to drill any holes through the firewall but this might be the exception.

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8 minutes ago, Mark Shaw said:

Morgan, 

    Have you ever held your finger on the end of a straw & pulled a straw full of liquid?

 

 

 

Yeah. Now replace that with a Marvel Mystery Carburetor at the bottom of the straw.

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