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Old 01-03-2015, 10:41   #1
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New gas tanks.

I bought a new external gas tank for a small outboard I recently acquired. It is the new style without a vent that is apparently designed to allow pressure within to increase with temperature to keep fuel vapor out of the atmosphere. Problem is that the outboard is not expecting pressurized fuel and it leaks fuel in some situations. I've been trying to remember to detach the hose when the boat will be waiting for me on hot days with the motor tilted out of the water. Any others with this experience and possible solutions? Hoping no EPA rants, just solutions.

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Old 01-03-2015, 10:50   #2
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Re: New gas tanks.

The vent is still there on the fill cap (at least mine is) I had the same problem, pull the cap off and pull with small pliers the one way check valve that doesn't allow pressure out but allows air in, now the little screw cap on the vent acts like it always has.

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Old 01-03-2015, 11:43   #3
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Re: New gas tanks.

  • It should not leak if the needle valve is good.
  • There isn't a fuel cut-off valve on the engine? Add one in the line somewhere, as this is really a necessary safety requirement, even without the sealed tank. There should ALWAYS be a cut-off valve.
  • While the pressure build-up is alarming, remember that it is doing you 2 big favors: it is reducing volatile loss (more volatiles = easier starting and less gumming), and it is eliminating most fuel oxidation and all water absorption by eliminating breathing.
In my experience you will have less fuel problems with these tanks and with outboards with built-in tanks if the vent is kept closed. Do close the fuel cut-off valve. Some will say disconnect the hose and let it run out of fuel, but that is a different thread.

I would probably crack the cap to let the pressure out before running, if leaks were a problem, but I would NOT make any change, as sail monkey suggested, that prevents sealing the tank (unless I misunderstand and the tank can still be sealed). You might be solving a short term problems and creating a long-term problem.
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Old 01-03-2015, 13:13   #4
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Re: New gas tanks.

No vent screw, period. Don't know how make-up air gets in, but it does, somehow.

I think the pressure inside the new tank must sometimes be higher than the needle valve (carb float valve) is expected to seal against, because it all works fine in most conditions.

Do most OBs have internal shutoff valves for their external fuel lines? I never noticed that. Easy enough to unclick and pull out the hose connector. Problem is remembering to remove and to replace it. As it happens this OB has a valve to turn off the internal tank, but it does not block the external line in either position. It tees in after the valve.

Sounds like my workaround may be my best option. Glad to know the good reasons for the new tank design.

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Old 01-03-2015, 13:32   #5
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Re: New gas tanks.

Best plan is to disconnect it, and let the engine run until it empties the carb, unless of course your using it daily

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Old 01-03-2015, 16:24   #6
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Re: New gas tanks.

I think marine stores have solutions for your problem. Something that's inserted in the fuel line or at the end of the fuel line. I've seen them on TV but never paid close attention. A visit to West Marine of a store that deals in smaller outboard powered boats should find you a solution.

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