Where is the vent in the fuel tank?

[RDJuhl]

Hi,
Everyone on this forum have been very helpful...many thanks.

My father-in-law has a 1986 15 HP Seahorse which cold starts fine, but has difficulty on warm re-starts. We were discussing whether the fuel tank vent is open...he has a metal tank like the one pictured, but I do not see a vent. Is there a vent in one of the connections? When we open the cap, we hear pressure releasing from the tank.

1986 J15ECDE 1986 Evinrude / Johnson Johnson Outboard FUEL TANK WITH GAUGE Diagram and Parts

http://www.boats.net/parts/search/BRP/JOHNSON/1986/J15ECDE 1986/FUEL TANK WITH GAUGE/parts.html

 

[Sixmark]

Re: Where is the vent in the fuel tank?

The vent is usually in the cap, there will be a thumb screw in the center of the cap that you turn counterclockwise to open and slockwise to close

 

[RDJuhl]

Re: Where is the vent in the fuel tank?

That is what I thought, as my plastic fuel tanks for my boat have the thumb screw. However, in my father-in-laws fuel tank, there is a metal cap...no thumb screw. I am not finding any vent...and we hear pressure releasing when we open the fuel cap.

 

[chaincase]

Re: Where is the vent in the fuel tank?

Those old style metal cans have self venting caps, alot of people prefer them to plastic. Not sure if it can really fail or not but I know it it possible to find replacement parts for them if you want to be sure. Or just loosen the cap up to aid in your diagnosis.

 

[Sixmark]

Re: Where is the vent in the fuel tank?

86 isn't that old, it may be as simple as a wrong cap. My 77 and 84 both have screw vents

 

[boobie]

Re: Where is the vent in the fuel tank?

The vent is in part# 16 of your diagram. If everything is correct in it, when you plug your fuel line to the tank it it automatically vents the tank. There was a reason OMC built them that way. If the tank wasn't venting the primer bulb would colapse when running the mtr.

 

[RDJuhl]

Re: Where is the vent in the fuel tank?

Thanks everyone for the comments. Boobie...one follow up...IF the vent is working, and if the boat sits for a couple days, , would we hear pressure releasing when we open the gas tank? In other words, is it a one way vent, allowing air into the tank as you burn up the fuel, but not allowing gas pressure out of the tank when it sits for a couple days?

 

[boobie]

Re: Where is the vent in the fuel tank?

As long as you have the fuel line attached to the tank it's vented. OMC built it that way so when you hauled your tanks to town for fuel in the back of your "station wagon", you wouldn't have fuel vapors escaping from the tank when you lit up a cigarette.

 

[Tim Frank]

Re: Where is the vent in the fuel tank?

My OMC fuel tanks have a two-position cap. If it is tightened fully, it is sealed tight. That would be for transport or storage between uses.
If you unscrew it 1/4 turn, then there is venting.

 

[emoney]

Re: Where is the vent in the fuel tank?

Doesn't most times the vent issue cause the motor to die while running, instead of a restart issue? Could just need a new primer bulb. On cold starts he's pumping it, warm starts he's not I'd assume. They can go bad, speaking from experience, lol.

 

[boobie]

Re: Where is the vent in the fuel tank?

Tim, do you unscrew your cap everytime you use the mtr?? The reason for the two position cap was to relieve pressure in it before taking it off . IE: sitting in the sun.

 

[Tim Frank]

Re: Where is the vent in the fuel tank?

No, I just leave it in the "middle" position.
I've always done this and it has worked, but maybe that is not the proper method....

Do you want that pressure to build up? I would have thought that if it was vented, the pressure would not build.

I've had a motor quit because I had the cap fully tightened. When i opened it to the mid-position, you could hear trhe inrush of air break the vacuum.

 

[boobie]

Re: Where is the vent in the fuel tank?

Do you disconnect the fuel line from the tank when not using it??

 

[Tim Frank]

Re: Where is the vent in the fuel tank?

Not usually.

 

[boobie]

Re: Where is the vent in the fuel tank?

Did a little research. There is an air disc valve in the tank in item 16 that lets air in only when the mtr is running with fuel line connected. If the fuel line is connected when not running if this disc is working okay there is no vent for the tank. That's the reason for the pressure build up. When running, the tank is vented because of the fuel line connection opening up air to the disc and the tank.

 

[Tim Frank]

Re: Where is the vent in the fuel tank?

Did a little research. There is an air disc valve in the tank in item 16 that lets air in only when the mtr is running with fuel line connected. If the fuel line is connected when not running if this disc is working okay there is no vent for the tank. That's the reason for the pressure build up. When running, the tank is vented because of the fuel line connection opening up air to the disc and the tank.

So is what I have always though was an "intermediate" position just a phantom?:facepalm:
But I am not sure I understand how the fuel line is venting the tank? Fuel line should not be allowing air or fuel out...or air in.

 

[RDJuhl]

Re: Where is the vent in the fuel tank?

Thanks for the info on the fuel tank venting. If part 16 does the venting when the motor is running, then we will look elsewhere for the problem related to warm starts.

 

[boobie]

Re: Where is the vent in the fuel tank?

Tim, when you attach the fuel line to the tank the CONNECTOR pushes in those two little prongs you see sticking out. This gives you the venting and fuel flow. Look at part # 16 closely

 

[boobie]

Re: Where is the vent in the fuel tank?

RDJuhl, as I said earlier in the thread, if your tank wasn't venting when running WOT and your primer bulb collapses, then the tank isn't venting.

 

[Tim Frank]

Re: Where is the vent in the fuel tank?

Got it, thanks. Engine end doesn't have them....light goes on...