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Old 06-14-2011, 05:22 AM
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Default Fuel tank venting

I've been having trouble filling my fuel tanks. The fuel would spit back up out of the filler and not take fuel on occasion. I find that the fuel system had been re plumbed so that the vent line is hooked into the overflow opening in the top of the filler neck. The vent hose had some access length in it an had a low spot after it left the tank which was creating a trap in the line so when I ran the boat in rough water the fuel would splash back through the vent at the tank and block the vent line. The way this is plumbed the tank cannot vent to the outside when the gas cap is in place. The engine is a Honda 4 stroke and runs fine.
My question is does the 4 stroke Honda's need to have sealed gas tanks.
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Old 06-14-2011, 05:56 AM
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Don't know about the sealed tank question but the issue you describe is somewhat common. Often it is the angle the boat sits on the trailer. If you blow hard into the overflow, it will push the slug of gas back into the tank and you can fill again.
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Old 06-14-2011, 06:02 AM
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Originally Posted by seebruce View Post
My question is does the 4 stroke Honda's need to have sealed gas tanks.
No. If you seal a gas tank, you won't be able to draw fuel out of it.

Redo the vent how the manufacturer designed it.
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Old 06-14-2011, 08:34 AM
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Originally Posted by seebruce View Post
I've been having trouble filling my fuel tanks. The fuel would spit back up out of the filler and not take fuel on occasion. I find that the fuel system had been re plumbed so that the vent line is hooked into the overflow opening in the top of the filler neck. The vent hose had some access length in it an had a low spot after it left the tank which was creating a trap in the line so when I ran the boat in rough water the fuel would splash back through the vent at the tank and block the vent line. The way this is plumbed the tank cannot vent to the outside when the gas cap is in place. The engine is a Honda 4 stroke and runs fine.
My question is does the 4 stroke Honda's need to have sealed gas tanks.
I think you are referring to a vented fuel fill. The pipe for the vent is not a fuel overflow, it is a vent. The cap actually has a 'valve' that lets the tank breathe. If your vent line has a low loop and gest gas in that loop, the vent won't work and the motor will starve for fuel. You need to re-route the vent line. A loop is OK but it has to face down (loop on top) and not up(loop on bottom)
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Old 06-14-2011, 10:55 AM
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I think you are referring to a vented fuel fill. The pipe for the vent is not a fuel overflow, it is a vent. The cap actually has a 'valve' that lets the tank breathe. If your vent line has a low loop and gest gas in that loop, the vent won't work and the motor will starve for fuel. You need to re-route the vent line. A loop is OK but it has to face down (loop on top) and not up(loop on bottom)
Thanks, I originally thought the same thing but can't see anywhere the gas cap can vent. What puzzles me is that the boat has the hull vent outlet with the hose and the tee still hanging there. I can't understand why it would have been changed.
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Old 06-14-2011, 10:58 AM
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Thanks, I originally thought the same thing but can't see anywhere the gas cap can vent. What puzzles me is that the boat has the hull vent outlet with the hose and the tee still hanging there. I can't understand why it would have been changed.
Well, it doesn't work so why not put it back and try it as designed?
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Old 06-14-2011, 11:57 AM
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Thanks guys, After calling everyone under the sun I finally found that lostsinker is right the gas cap I have is vented.
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Old 06-14-2011, 12:16 PM
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It's really the deck fill the cap screws into that is vented, isn't it?
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Old 06-14-2011, 03:21 PM
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It's really the deck fill the cap screws into that is vented, isn't it?
The vent line from the tank is connected directly to what I would call the overflow opening in the filler neck. The only way it could possibly vent when the cap is in place is through the cap itself.
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Old 06-14-2011, 04:38 PM
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Originally Posted by seebruce View Post
The vent line from the tank is connected directly to what I would call the overflow opening in the filler neck. The only way it could possibly vent when the cap is in place is through the cap itself.
And that is how it works. Assuming of course that the cap hasn't been replaced with a non venting cap.

Note that the venting cap is only venting when drawing fuel out of the tank to run the engine. When you remove the cap to fill the tank, the venting is through the fuel filler itself. If you're dealing with one of the gas station nozzles with the rubber bellows that pushes against the fuel fill, back it up a bit so air can get out. Or, use another gas station.
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Old 06-14-2011, 04:40 PM
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Is this what you have?


http://www.iboats.com/Perko-Combinat...view_id.237346

Quote:
Combination Gas Fill & Tank Vent - Perko
Quote:

Part # 0540DPGCHR
Integral tank vent with flame arrestor and anti surge valve. Deck plate key included. Chrome plated bronze cap with plastic base. Angled neck and heavy duty stainless steel bead chain. Ground wire required. For fuel hose 1-1/2". For vent hose 5/8". Neck length 2-7/16"
Note: I see from the description that there's an "anti surge valve" built in to the gas fill. It's possible that this valve is stuck or gummed up and this is what is causing your problem.
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Old 06-15-2011, 04:37 AM
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Originally Posted by rwidman View Post
Is this what you have?


http://www.iboats.com/Perko-Combinat...view_id.237346

[b]

Note: I see from the description that there's an "anti surge valve" built in to the gas fill. It's possible that this valve is stuck or gummed up and this is what is causing your problem.
Yes this is what I have except it's the straight fitting. I saw this in the description but didn't realize that an anti surge valve was a vent. Nowhere in the description did I see it say vented cap. What is realty amazing is that even the first person I talked to at Perko told me that the cap didn't vent.
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Old 06-15-2011, 04:48 AM
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Originally Posted by seebruce View Post
Yes this is what I have except it's the straight fitting. I saw this in the description but didn't realize that an anti surge valve was a vent. Nowhere in the description did I see it say vented cap. What is realty amazing is that even the first person I talked to at Perko told me that the cap didn't vent.
It's possible the person you talked to didn't understand the question or what product you had. It's also possible that he or she has no business talking to customers about technical issues.

If you can, disconnect the vent line from the connection to the fill fitting. Tape the hose to the fitting but don't block the opening.

Fill the boat and see if you still have a problem. If not, your problem is with the valve in the fill fitting. Fix it or replace it.

If you're still having a problem, it's time to check the vent hose and how it is routed in the boat. It needs to go "uphill" all the way. any dips will fill with fuel and block the venting.
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Old 06-15-2011, 05:25 AM
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Originally Posted by rwidman View Post
It's possible the person you talked to didn't understand the question or what product you had. It's also possible that he or she has no business talking to customers about technical issues.

If you can, disconnect the vent line from the connection to the fill fitting. Tape the hose to the fitting but don't block the opening.

Fill the boat and see if you still have a problem. If not, your problem is with the valve in the fill fitting. Fix it or replace it.

If you're still having a problem, it's time to check the vent hose and how it is routed in the boat. It needs to go "uphill" all the way. any dips will fill with fuel and block the venting.
Problem solved. Thanks for all your input. Just goes to show you learn something new every day.
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Old 06-15-2011, 05:34 AM
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Problem solved. Thanks for all your input. Just goes to show you learn something new every day.
Are you going to keep us in suspense?
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Old 06-15-2011, 06:10 AM
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Are you going to keep us in suspense?
I rerouted the vent hose to eliminate the low spot which was my initial problem. Now that I know that the system vents through the gas cap I have no more problem.
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Old 06-15-2011, 06:12 AM
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Originally Posted by seebruce View Post
I rerouted the vent hose to eliminate the low spot which was my initial problem. Now that I know that the system vents through the gas cap I have no more problem.
Glad to help.
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Old 09-13-2014, 08:02 PM
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Originally Posted by lostsinker View Post
I think you are referring to a vented fuel fill. The pipe for the vent is not a fuel overflow, it is a vent. The cap actually has a 'valve' that lets the tank breathe. If your vent line has a low loop and gest gas in that loop, the vent won't work and the motor will starve for fuel. You need to re-route the vent line. A loop is OK but it has to face down (loop on top) and not up(loop on bottom)
I have the Perko vented fill, can't fill the boat, gas just sits on top. The installation instructions says the vent system requires that the surge valve feels loose in order to operate properly. Is it this little cap inside the gas fill next to the gas cap chain? It's tight, meaning it won't turn using my fingers. Have not tried power tools on this, LOL. Do I loosen it like a screw on cap, it is just clogged. Any ideas?

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Old 09-13-2014, 10:09 PM
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Originally Posted by buellwinkle View Post
I have the Perko vented fill, can't fill the boat, gas just sits on top. The installation instructions says the vent system requires that the surge valve feels loose in order to operate properly. Is it this little cap inside the gas fill next to the gas cap chain? It's tight, meaning it won't turn using my fingers. Have not tried power tools on this, LOL. Do I loosen it like a screw on cap, it is just clogged. Any ideas?

That looks like the end of the vent coming from the tank. Sounds like you may have the same problem as the OP. Something wrong with the vent hose. You don't do anything with that little "cap" in the fill.
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