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Petrol tank vacuum

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by dbrain, Jan 6, 2016.

  1. #1 dbrain, Jan 6, 2016
    Last edited: Jan 6, 2016
    Hey guys,

    I'm back for another, way too frequent, dumb question.
    Recently my bike ('14 Street Triple) has had a bit of suction on the petrol cap when I go to fill up. I don't have to fight with it to get it open, but it requires a fair bit more force than in the past.

    Googling tells me this might be a "blocked vent". Is this a thing on newer bikes? How do I check something like this?
    Some people say their bike got to the stage where the vacuum was denting the tank.

    I think it may have started after I installed a Scottoiler. During the install the tank was full, and was lifted, making some petrol come out of the overflow tubes. Could this have blocked something?


    * Ok I googled a bit more and there's a bit around on the topic. So I probably jumped the gun asking the question.

  2. It is not so hard to pinch or kink the vent/overflow hose on some bikes in fitting the tank.

    Also, this time of year, if an open hose is left exposed for any length of time, certain wasps have a tendency to wall off the end to lay eggs in.

    Two possibilities.
    • Agree Agree x 2
  3. Haha. That sounds fun. Bike does stay outside a lot.

    Thanks for the tips. Figure I'll have a quick look tonight, from cap down to the visible parts of the tubes and hopefully see something obvious. If not and it doesn't get worse might see if it can be looked at as part of service (without costing $38949020)
  4. Don't ride with a bloked or partially block tank vent. It will cause you to run lean and that can cause serious engine damage.
  5. #5 dbrain, Jan 6, 2016
    Last edited by a moderator: Jan 6, 2016
    I only just learnt that's probably what it is. I'm going to assume partially blocked, as it isn't some crazy amount of suction.
    Will make sure I open the tank before riding to at least equalise the pressure before I get it sorted.

    Hopefully it's something obvious I can fix tonight.

    I take it the air vent tubes coming from the tank are also used for overflow? So if the tank isn't really low on petrol it will get messy if I lift it and have them disconnected?
  6. Got a manual? There should be something in it about these tank's hoses.
  7. Had same problem on my Street triple after it came back from a service. There are several rubber tubes running under the tank. One is for venting. The tube was pinched when they put the tank down after the service. Fairly easy to fix, just lift the tank again and make sure all the hoses are clear when you lower is again.
  8. Eyyy! Thanks guys. It was the same issue that ultramultram had. Except I was the incompetent mechanic. When I put the tank back down after installing the scottoiler I've managed to place the tube in a way that it was pinched a bit.

    Oh funny method for testing if you ever think you have this problem. Bike pump, hold the nozzle on to the air hole under the petrol cap until it forms a connection.. push (hard doing it solo, so find a friend if you can to hold the nozzle or pump the pump).
    If it goes through easy all is well.. if it struggles the tubes probably blocked.
    • Like Like x 1