Gas leaking from tank vent after ignition turned off

Discussion in 'The Bench' started by 70skylarkcusto, Jun 11, 2017.

  1. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    well, the title pretty much says it all.

    After some time not running, my skylark is finally back together with an entirely rebuilt drive train and running like a top. Took it to a show this weekend then around town almost all day. When I got home and turned off the ignition I heard some gurgling noises which I assumed was gas draining back to the tank, however when I looked under the car I noticed a small puddle of gas under the passengers side front of the gas tank.

    Took the car out again today and the same thing happened when I got back home. Not sure if it happens every time drive or only after the car has been out and really up to temp. Any ideas what might cause this and how to prevent it?
  2. buick64203

    buick64203 Just plum crazy Staff Member

    Are you running a return line? And is the gas cap vented? And do you have the two rubber vent lines and filter hooked up?
  3. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    I am running a return line. There are the two lines that run to the fuel pump, 2 vent hoses at the tank, which I've never touched (I didn't have this issue before the rebuild) everything is as it was. But where should the filter be? I have an inline filter running to the carb from the pump?
    However it may also be interesting to note I'm having hard starts after the car sits for even a day as if the carb is empty. The q jet was also rebuilt and there is no visible leaks on the intake to lead me to suspect the bowl is leaking. Not sure if fuel could be being drained back from the carb as well.
  4. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    Gas cap is stock, so I'm not sure if the stock caps were vented or not
  5. bostoncat68

    bostoncat68 Platinum Level Contributor

    Well that front corner is where the vent hoses for the tank should be connected. (I have two in my 1968 Wildcat- two different sizes??) I believe that in 1970 most GMs still just had those couple of hoses pointed north to vent the tank. (There are some little "hooks" by the wheel spring that retain them...pretty simple) However, 70 was the year California cars first got an EVAP system -- basically a carbon cannister behind the rear seat that the vent hoses connected to (vs open air) to capture some of the fumes (and the stank...). In all case, as the tank expands and contracts (it changes WAY more than you think) the vent hoses would normally keep fuel from dribbling out. If they are not in-place or maybe actually pointing down towards the ground, fuel may come out... I would start by looking to see if the hoses are there, connected and if they are pointed up... Seems likely that when your new drivetrain was installed they were disconnected, removed or left dangling down. In all cases, it should be a quick fix. Just be attentive that the fumes are far more flammable than the gas itself so don't start drilling holes or something that might create sparks...
  6. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    Thanks for the reply, I was actually under the car installing a rebuilt rear end about 2 weeks ago and I know for a fact the hoses are indeed pointing up and there is no canister, they vent to open air.
    bostoncat68 likes this.
  7. Rob Ross

    Rob Ross Well-Known Member

    While the fuel is leaking out, have you tried to remove the fuel cap? If you do, use a rag in case it tries to come out. If you hear a pssssst, something is wrong with your vent system.
  8. flynbuick

    flynbuick Super Moderator Staff Member

    The surge tube is missing from the top of the vent hoses. They are reproduced. 70 models are more prone to do this especially when parked on non-level ground.
    Last edited: Jun 12, 2017
  9. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    I will look into the surge tube and maybe getting a vented gas cap. But this is happening when the car is parked on level ground. Is it at all possible I switched the two fuel lines going to the fuel pump? Would this make any sort of difference trying to switch where the lines are hooked up to?
  10. Briz

    Briz Platinum Level Contributor

    I do not believe it is possible to switch the lines at the pump. Should be 2 different sizes and the return line would not pull from the sender/ bottom of the tank.Next time it does it remove the gas cap as soon as you hear the noise to see if its pressurized.
  11. 70skylarkcusto

    70skylarkcusto God, Country, Cars

    So, I found one issue was that the needle and seat in the carb, although it was just rebuild, is not the best and was allowing gas to run back to the fuel pump and consequently back to the tank. Not sure if this was the root cause of the issue, but I've installed a check valve between the fuel pump and carb and have not had an issue since.
    Thanks for the help

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