gas fuel tank venting, return lines, charcoal canister

Discussion in 'Troubleshooting & Diagnosis' started by efinger, Nov 9, 2012.

  1. efinger

    efinger Veteran Member

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    I thought it would be helpful to consolidate some info Ive recently read concerning fuel tank venting, fuel return lines and the charcoal canister. Im no expert so correct me if im wrong and Ill edit the post.

    Camaros came with two types of gas tanks, one type had two lines coming off of it, and the other had three.

    The three-line tanks have a fuel supply, fuel return line, and the line to the charcoal canister. The two line tanks dont have the return line.

    You dont generally need to run a return line if youre running a mechanical pump.

    You do need one (highly recommmended?) if you have an electrical pump.

    You must vent your tank in some way or you will have fuel delivery problems.

    To vent your tank you can either leave the line hooked to the charcoal canister or you can install a small breather filter on the end of the line somewhere and remove the charcoal canister. You may smell more fumes if you do this.

    You can also use a vented gas cap to allow air into your tank.
     
    Last edited: Nov 9, 2012
  2. clutch74

    clutch74 New Member

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    Hi efinger. I know this is an older post but I have a question about this and you seem to know what you're talking about.
    I have a 1971 Camaro SC that I am just about ready to drop my 489 into. I am using the FAST EZ-EFI setup and I have to have a return line. When looking at my tank, it has 4 line ports. The inlet port is on top of the tank.
    There is one on the drivers side pointing forward that I assume is for the charcoal canister. And there are 2 pointing forward on the passenger side of the tank. Is one of these to for a return line? Any info would be greatly appreciated!
     
  3. Rene Melten

    Rene Melten Veteran Member Lifetime Gold Member

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    The two on the pass. side and the one at the drivers are are all vents on a '73. Do you have a vapor separator behind the back seat under the car?
    Check this pic to see the question.

    [​IMG]
     
  4. jb451

    jb451 Veteran Member

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    I was wondering what that third line was in my new sender... My old one had two. Thanks!
     
  5. clutch74

    clutch74 New Member

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    Nope. Mine does not have the vapor separator. But all the vent lines in that illustration look just like mine. Someone has capped them all off. Perhaps that vapor separator was something they started after 71'? And I assume using one of the vent lines for a return line is probably not a good idea?
     
  6. mikes70

    mikes70 Veteran Member

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    mine had a vapor separator, stock 70 ss
     
  7. flowjoe

    flowjoe Moderator Staff Member Lifetime Gold Member

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    It's more complicated than all this...although Rene has nailed the key bits.
    1970 stands alone. There are two tanks. One 49 state tank and one CA emissions tank (NA-9). 49 state unit has a fuel feed line from sender and a vented cap. A return line is present on some models and will go through the sending unit. An NA-9 set up will have a sealed gas cap and the three vent lines in the tank body. It will also have a fuel vapor separator and a charcoal canister.
    1971 and up all tanks are the same....pretty much just like NA-9 set up above except vapor separator looks like the one in Rene's image above.
     
  8. giggity

    giggity Veteran Member

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    I know this is an old post, but Ive been researching return lines and thought Id comment on this.

    Flowjoe is correct, my 1970 only has one line coming out, and is vented through the gas cap. Im building a big block so my fuel requirements have changed. Im looking to use the stock tank, but Im changing the sending unit to one that has a return. Im using a electric pump with a return. I had considered using a return line from the regulator, but i figure its just a waste of travel if I can return from the pump which is by the tank. I will need to see how the tank can handle this, as I dont want the tank churning violently, but I think it will be ok.
     
  9. repoman79

    repoman79 Veteran Member

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    My return line got damaged , instead of running a new one can I use the canister line as the return? Since it's not currently hooked to tank or canister?
     
  10. 8pack

    8pack Veteran Member Lifetime Gold Member

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    NO! The canister line is really just a vapor recovery line and it goes back to a very small almost pin hole at the tank. Way too small to allow fuel to return to. I looked at the same thing and had a spare tank to look at. I just used the stock 1/4" return line down by the fuel pump and for my set up that worked fine.

    EDIT: If you mean can you the actual hard line from the canister and reroute to the return port on the top of the tank, YES. If you want to use that line connected to the original location for the charcoal canister, NO
     

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