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#568086 - 06/09/17 10:08 PM Tank Venting Question  
Joined: Jan 2003
Posts: 531
hawkshaw Offline
hawkshaw  Offline

Joined: Jan 2003
Posts: 531
My brother in law has a brand new Godfrey Poontoon boat. It has an outboard engine (Yamaha 90). The issue is it's pulling a vacuum on the fuel lines and the pump bulb is collapsing. It has the new EPA gas vapor system on it that has two check valves that only let pressure flow out but not in. When the boat uses fuel how is the loss of volume and subsequent negative pressure (vacuum) supposed to be compensated. The fuel cap appear to seal it off tight.



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#568116 - 06/12/17 12:35 PM Re: Tank Venting Question [Re: hawkshaw]  
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Lowrider78 Offline
Lowrider78  Offline

Joined: Jan 2004
Posts: 1,834
Newton Ks
Loosen the tank cap and see if the problem stops.

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#568118 - 06/12/17 02:10 PM Re: Tank Venting Question [Re: hawkshaw]  
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captkevin Offline
captkevin  Offline

Joined: Oct 2003
Posts: 7,443
Chicago, IL
If he bought it brand new I'd be letting the dealer make any repairs as to not compromise the warranty.

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#569675 - 11/16/17 02:41 PM Re: Tank Venting Question [Re: hawkshaw]  
Joined: Oct 2014
Posts: 124
Boatbottom Offline
Boatbottom  Offline

Joined: Oct 2014
Posts: 124
Sacandaga Lake Mayfield, NY
Is this a portabe fuel tank? If so the valve built into the fill cap is a vacuum pressure relief valve. When the knob is roatedto the right it closes and seals the tank, preventing vapors or pressure from escapting. The valve is designed to open and vent pressure before the pressure can build enough to burst or damage the tank. When it's time go for a ride, the valve should be rotated to the left midway between fully closed and all the way "open". This allows the vacuum portion of the valve to operate allowing air to enter the tank and preventing a vacuum from forming.

I have a couple of plastic six gallon portable tanks on the pontoon boat. When the valve is closed the tanks expand and looks like they are about to burst. I've discussed this with Moeller and that's where I got my information. I don't know the part number or if it is still available. They were allowed to sell replacemet caps for older tanks. They had the samefiller cap thread as the new tanks which would allow you to avoid the vacuum, pressure issues.

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