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  1. #1
    Join Date
    Nov 2011
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    12

    Fuel system venting

    Hello...Iím trying to plan out how Iíll be doing my fuel tank vent system on my mustang. I have a Ricks efi tank, ridetech fuel cap, and will be ordering II much fabrication vent canister. I need to install a rollover valve and thatís where I get confused. The filler neck in mustangs is the highest point in the fuel system. Meaning if the tank is full there will be fuel up in the filler neck. If I screwed a rollover valve directly into the tank bung (covered in photo with painters tape) it would be pushed shut by fuel trying to entire vent line to height of fuel in filler neck. Could it be screwed into II much canister feed line port as the canister will be mounted up as high as possible? Or for this issue is that what discriminator valves are for?

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  2. #2
    Join Date
    Sep 2010
    Location
    Beach Park IL
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    Mustangs are tough. In a perfect world, you would have a vapor dome on the top of the tank and the vent line would be in there.

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    The vapor dome is higher than the tank can get filled, so that eliminates the need for a fluid/vapor separator. The separators were used on cars when charcoal canisters first came into use. They do exactly what they sound like, allow liquid fuel to escape the tank but prevent it from reaching the charcoal canister. Design wise, they are just like a cheap radiator overflow tank but in reverse. The IIMuch cans do have some capacity to them, but it is not enough in the very specific case of filling the tank full, right to the vent, and then parking the car.

    You can:

    A. build a separator and plumb that inline between the tank and II Much vent.

    Dos. Not fill your tank unless you are planning on driving it.

    Triangle. Build a dome on top of your tank

    For. vent from the filler neck. Note: not venting the actual tank can affect the filling process.

    Personally, if I can, I engineer the fuel tank so that it can not be filled all the way and make sure the vent is on the very top and it usually works. I have built and used separators when plan A doesn't work.
    Donny

    Support your local hot rod shop!

  3. #3
    Join Date
    Nov 2011
    Posts
    12
    Is a separator the same as a discriminator in-line valve?

    I ordered a surge/spit back flapper for the filler neck at the tank. This should keep fuel from when filling tank to fill the fill tube with fuel.

    The ridetech (believe vaporworks makes it?) fuel cap housing has a bung for a vent. So that’s an option. But with flapper valve at tank filler it would be shut except for when fueling. So wouldn’t allow venting. Or skip the flapper valve and T cap vent into vent from tank as described below?

    Thoughts on running line out of tank vent bung up as high as possible. 90 over along rear tail lamp panel to drivers quarter with in-line discriminator valve. Then 90 up into in-line rollover valve screwed into II much fabrication vsr canister. Then outlet from canister goes out through trunk floor behind drivers rear tire?

    And does the outlet need to be lower then lowest point of the fuel tank?

  4. #4
    Join Date
    Nov 2011
    Posts
    12
    https://www.fillernecksupply.com/2-i...35002-0635dp2/

    This is the filler neck flapper i mention.

  5. #5
    Join Date
    Sep 2010
    Location
    Beach Park IL
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    2,389
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    I do not see a need for the flapper. Blow back out of the fuel fill is almost always improper venting or improper fill neck design.

    I "think" if you ran a line from the tank up to a TEE, one side of tee goes to filler neck, other side of tee goes to II Much can that it would work just fine. The line to the can needs to run level or uphill with no low spots to trap liquid.
    Donny

    Support your local hot rod shop!

  6. #6
    Join Date
    Nov 2011
    Posts
    12
    Sounds good. I’ll get it plumbed and post a follow up here.

    No need for a discriminator valve that you see?

    And could the rollover valve be plumbed into the exit line out of the II much canister? The in-line rollovers are pretty long and I’m afraid screwed in at canister inlet it would make the incoming line low/dosnhill