Fuel Tank Vent

Discussion in 'The Garage' started by RMac, Sep 29, 2019.

  1. RMac

    RMac Cheese!

    Joined:
    Aug 23, 2004
    Oddometer:
    1,860
    Location:
    Stumptown
    I have no experience with this but I suspect my Cagiva Gran Canyon fuel tank vent is plugged. The hose is clear, but I think the fitting may be plugged. I've read various forums suggesting running a stiff wire, or even a small drill bit up the fitting. Before I go gonzo, I thought it prudent to ask: Is this a check valve, ball valve type thing? Or does it run straight through into the tank?

    Here's a pic of the fitting which is located underneath the left side tank:
    Canyon-vent-fitting-IMG_4829.JPG
    #1
  2. unfocused_adventure

    unfocused_adventure Not my circus, not my monkeys... Supporter

    Joined:
    Oct 1, 2019
    Oddometer:
    58
    Location:
    Auggieland FL.
    normally if it comes "through" the tank:

    1 - it's a water drain for the filler (if applicable)

    If it's a vent then there should be a hose running up to the vent assembly. I'm not familiar with that bike but on my BMW or my old Triumph which are both fuel injected. They internally had a hose and vent that exited the tank. So poking a stiff wire might do more damage.

    If you have a flat fuel cap open it up and look for a water drain hole around the perimeter. This has to drain somewhere and on both the above mentioned scoots the hose went through the tank.

    Pics are of my 94 R1100RS as well as other BMW's
    The second pic, lower left corner is the vent. the hose from it runs down to the fuel pump plate and then exits.
    Think before you shove anything in a hose, it could lead to a massive fuel leak
    Hope this helps





    plate.jpg download.png
    #2
  3. usgser

    usgser Long timer

    Joined:
    Nov 6, 2005
    Oddometer:
    3,503
    Location:
    Westside WA
    Not familiar with your bike but likely its a tank vent/overflow. Should be straight through pipe into the tank up high above the fuel level. Ends at/near the fill pipe throat. No check valve etc. On older bikes the fitting will have a hose that runs down below the motor so it doesn't overflow on the motor or exhaust. Newer bikes the hose will go to an EPA charcoal evap canister. What makes you think the tank isn't venting? If it can't breath it'll pull a vacuum on the tank if no air to replace the fuel used up and the fuel flow will stop and the motor quits. Easy to tell. When the motor quits remove the gas cap and you'll get a woosh sound as air rushes into the tank.
    #3
  4. RMac

    RMac Cheese!

    Joined:
    Aug 23, 2004
    Oddometer:
    1,860
    Location:
    Stumptown
    Thanks, problem solved. Vent / overflow was plugged.

    This bike has a plastic / composite tank (actually 2 split tanks). The vent / overlfow passageway from the filler is molded into the plastic and exits though the metal fitting shown above. A rubber hose attaches to the fitting and exits under & behind the engine.

    At the advice of my mechanic, I used a piece of twisted safety wire and carb cleaner to slowly remove the clog. I was told this is fairly common and results from ethanol gas evaporation. Pain the ass but problem solved.
    #4
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