OMC single hose tank question

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Adam1961
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OMC single hose tank question

Postby Adam1961 » Wed Sep 06, 2017 8:05 pm

I have never really given much thought to the single hose tanks as the usually provide trouble free service as long as they hold fuel. I have one that is starving a 40hp motor and requires investigation. The motor in question is a 1960 40 hp with freshly rebuilt fuel pump. It runs great on one of the tanks in the boat, but starves on the tank in question.

When looking at the housing mounted on the tank, I see the two spring loaded pins on the connector face and a round check valve on the underside. I would assume that the check valve lets air in as fuel is consumed. What is the function of the pins on the connector face? Does one close the "out" passage when no hose is connected? What does the other do? When I connect my fuel line, it seems to leave a fairly large gap from the connector face to the face of the fitting on the fuel hose. It looks to be an OEM fuel hose. the motor starts well when the bulb is squeezed and then runs out of fuel. Pumping the bulb keeps it going. The pickup tune and screen look to be in good condition. What is the most likely issue here?

Adam

Chris_P
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Re: OMC single hose tank question

Postby Chris_P » Thu Sep 07, 2017 6:11 am

Does this tank have a vent, or is it one of the eco friendly models! Sorry, but I hate the tanks without a manual vent, and have seen them starve motors more than once!

Adam1961
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Re: OMC single hose tank question

Postby Adam1961 » Thu Sep 07, 2017 9:35 am

The cap does not look vented. There are rubber gaskets under the cap and they seem pretty tight when closed. These are the original 1960 tanks, not replacements

Dougs Outboards
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Re: OMC single hose tank question

Postby Dougs Outboards » Thu Sep 07, 2017 10:44 am

Maybe I am misunderstanding here, but are you talking about the old steel single line tanks? They have 3 positions for the cap. Closed, vented, and open. If you close the cap all the way (to the right), then turn it left one "click" it will be kinda loose and sloppy, in a middle position, letting air in, but you cannot lift the cap off til you turn it all the way left one more click. Run it in the middle position, close when finished. Try that on your cap you will see what I mean. Hope this answers your question.

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Fisherman6
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Re: OMC single hose tank question

Postby Fisherman6 » Thu Sep 07, 2017 11:12 am

The steel OMC single line tanks with the male fitting at the tank and the two pins are vented when the fuel hose is connected. That is assuming the valves are working properly. The two pins are an air vent and a fuel shut-off. With the cap fully closed and sealed it is supposed to be completely closed off and it should not allow fumes or fuel to escape. When the hose is connected the fitting depresses the two pins and opens the fuel flow as well as allows air into the tank to allow fuel to be drawn out. I have a few of these tabks and they all leak at the valves in the fuel fitting, but that is how they are supposed to work.
-Ben
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FrankR
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Re: OMC single hose tank question

Postby FrankR » Thu Sep 07, 2017 11:20 am

OK, here's the deal. The two pins in question seal off the vent and fuel outlet when the hose is removed. Attaching the hose pushing the pins in, and opening the vent and fuel outlet. The vent, when open, is a one-way vent on all but the earliest tanks. That means it allows air to enteer but does not let fuel and air to slop out. It appears you have the one-way vent. The fuel outlet pin is a simple open-or-closed valve. Push it in and fuel can flow, remove the hose and the fuel cannot flow out.

The most common problem is leakage around the fuel pin (and it is a common problem). If it leaks around the pin, your fuel pump sucks air from the leak path, instead of fuel from the tank.

If you look at the fuel pin, you will see a tiny brass washer surrounding the pin. The washer is retaining a tiny o-ring inside. So, if it is leaking, you need to replace the tiny o-ring. That is done by removing the core plug from the back side and sliding the pin and spring out. Now stick a punch into the washer and rock it back and forth to break the washer free. Now you can pick the o-ring out and replace it. You can re-use the washer. Use a hammer and screwdriver to stake it back in.

There are more o-rings acting as valve seats. Might as well replace both of those while you are at it. Of course you will need all the o-rings and core plugs.

Be aware there are two sizes of the tiny o-ring. The very early tanks had the smaller size.

FrankR
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Re: OMC single hose tank question

Postby FrankR » Thu Sep 07, 2017 11:48 am

1958-1960 Fuel tank (small o-ring on vent pin)

Image

1961 Fuel tank (large o-ring on vent pin and one-way vent valve)

Image


Image

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Wedgie
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Re: OMC single hose tank question

Postby Wedgie » Thu Sep 07, 2017 12:10 pm

Here's Art S's write up on how to repair the single line tank.


http://www.oddjobmotors.com/tt4_singlelinetanks.htm

Adam1961
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Re: OMC single hose tank question

Postby Adam1961 » Thu Sep 07, 2017 12:30 pm

Ok Guys. Now I think that I have an understanding of how the tanks are supposed to work. It seems that the valves on my tank are working as they should, as I get pressure or vacuum in the tank when moved to a warm or cold space with the cap shut.
This tells me that it is unlikely that the vent it not allowing air into the tank to replace the fuel consumed...UNLESS my fuel line is not pressing the pin in far enough. It is more likely that it is drawing air through a leak and breaking the supply of fuel. Would that most likely be the O-ring behind the Fuel pin that Frank mentioned?

outbdnut2
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Re: OMC single hose tank question

Postby outbdnut2 » Thu Sep 07, 2017 1:10 pm

You can bend the edge of the spring loaded release clip that holds the line connector to the small post on the tank so it pulls the connector farther up against those pins. I have only seen this as an issue once.
Dave


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