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What's the tube which goes from the fuel tank on race bikes?

Discussion in 'Racing, Motorsports, and Track Days' started by syd rs125, Feb 13, 2008.

  1. What does it do ??
    and where does it go? All i can see is it goes into the front console somewhere.
    Why don't we have it on road bikes it looks trick as.
    If you have no idea what i'm talking about here is a pic of the nsr 500 which has the tube running from the tank and into the instrument pannel somewhere.


    Probably something really simple but i have been curious for ages.

  2. That tube is the fuel tank breather.
  3. and what does a fuel tank breather do??
    does it have something to do with ram air??
  4. No, ram air is the ducting that feeds air into the airbox.
    That tube allows air to enter the fueltank, to replace the fuel as it is burnt. If the tank was sealed, a vacumm would occur, and the fuel would not feed to the engine. Your streetbike has a small hole in the cap, to do the same job.
  5. Ahh i see so this tube on a race bike is just an improvement on what we already have on our road bikes.
    Does it have any significant advantages??
  6. Yeah. When a bike with a full tank is on the grid, there is a fair bit of heat coming up from the engine. this expands the fuel, pushing it up that clear length of hose. This gives a visual early warning that a spill is about to happen.
  7. Which is why this rule is in place i guess.
    So the non return valve makes fuel that comes out of the fuel tank not go back into the tank but into this suitable container??

    2.6.2 Fuel tank breather pipes must include a non-return valve. Fuel tank breather pipes must discharge into a suitable container, one per motorcycle with a minimum capacity of 200cc and a maximum capacity of 250cc.

    Thanks alot for your response MVrog pretty interesting stuff.
  8. "fuel tank breather hose" pffft

    That's what they'd like you to believe.

    It really goes to the container that the elf lives in that cranks your engine over. and they don't fill up with petrol, but a cocaine solution.

    I should know. My bike has one.
  9. Dirt bikes have had this for years. It's to stop a vacuum forming in the tank when the fuel goes down. If it is just a vent on the top of the tank, it could let water get into the tank, so it leads down somewhere else to stop water running into the tank. At least that's what I've always thought they're for
  10. If you don't know the answer guys, you shouldn't make one up. He'll go and tell his mates now and come off sounding like a dill.

    That hose is used by the rider to adjust tyre pressures during the race, the rider either blows into it, or lets some out depending on what's required.
    This way they can keep the pressures at a constant for the duration of the race and reduce tyre wear. It was considered a major breakthrough in it's time.
    Modern day race machines have an automated system in place which is why you rarely see a hose being used nowadays.
    The team technicians use the onboard telemetry and computers to make the adjustments from the pits.
    As you can see in the picture above, the NSR is old school.
  11. Oh Cheffa I'm in tears!!! :rofl: :applause:
  12. No, it's not for the tyres. some riders used to blow in it to stimulate the elf, however. The tyre adjust tube was to be found in the riders seat.
  13. And they even named a brand of petrol in the Elf's honour in France :LOL:
  14. That is why baked beans is the breakfast of champions...
  15. Wrong way round.

    Air can get in but the one way valve prevents fuel getting out.
    Most road bikes have a vent built into the fuel cap. A small 1mm hole can usually be found.
  16. lol got some pretty funny comments here thanks for the feedback and i'll keep and eye out for that elf.
  17. Its a straw for a quick drink on the go :rofl:
  18. It's a Felching straw.
  19. I don't want to start a shitfight here but I believe that Chef and Ibast are both right and both wrong, (in a way).
    For many years, before the days of knee dragging, the Elf's job was indeed to crank the engine over. But, after the advance in tyres and ever demanding racing conditions it became neccessary to run a Constantly Updating Normal-pressure Tyre, or C.*.N.T on every bike. Yes, an unfortunate achronym, but a racing necessity non the less.
    As is to my understanding, specialized multitasking Elves were bred that could control engine cranking whilst maintianing the C.*.N.T system for the duration of a race.
    This all happened in the early Eighties when cocaine was relatively new to the Elves, but when South American cocaine trade started to step up in the mid eighties the Elves became more and more dependant and started to develop respiratory problems. To overcome these shortfalls manufacturers installed air tubes so that riders could supply extra air to the oxygen starved Elves and also to help blow out the hookers and empty beer cans that would invariably build up over the course of a race.

    Hope this helps :)