Crazy gas tank pressure?

Discussion in 'Parallel World (790/890)' started by Greg di, Mar 28, 2020.

  1. Greg di

    Greg di Been here awhile

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    This was the first day it got above 65 degrees since I got this bike and there is so much pressure developing in the gas tank that you can hear it trying it to vent when you kill the bike and then if you open the gas cap, it practically explodes.

    My buddy's does this too.
    What is the fix? This is dangerous.
    #1
  2. zaxrex

    zaxrex I don't know. Do you know?

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    Not a KTM owner, but sounds like a problem with the EVAP system. Because it's dangerous and emissions related, manufacturers should cover these parts for the lifetime of bike IIRC.
    #2
  3. Nowwhat

    Nowwhat I'll Go Second... Super Supporter

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    Evap cannister.

    Pull the hose... see if it resolves your issue..
    #3
  4. usgser

    usgser Long timer

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    When you remove the gas cap you sure it's pressure escaping and not air rushing in? If your tank vent is plugged as you use fuel air needs to replace the fuel or the tank will pull a vacuum and eventually shut down fuel flow. Either way you've got a vent/evap system problem.
    #4
  5. Greg di

    Greg di Been here awhile

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    How do you do that?
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  6. Greg di

    Greg di Been here awhile

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    It's air coming out for sure. The cap just about flys off.
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  7. Gaulin

    Gaulin Orange (& Blue) Crush

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    First easiest step is make sure the vent hose on the lower RH side isn't kinked and is free flowing. This is the one that connects to the plastic piece in the tank guard. The other end of this hose connects to the bottom of the cannister.

    Don't just remove this hose as then fuel trapped in the cannister will just drip directly down onto the exhaust.

    The next step is remove the cannister. Easy job, just takes a little longer and some more parts to remove. See Rottweilers video here:


    Note you don't have to use a dongle if you choose to just leave the valve in place and hooked up.
    #7
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  8. Mconnell

    Mconnell Adventurer

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  9. lowbrow

    lowbrow Adventurer

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    We call this fuel geysering with our chainsaws. Usually happens when it's hot outside. Engine and outside temps heats the fuel until it vaporizes and it builds pressure. It'll spew out half of the fuel in the saw! After you remove the cap and the fuel vapor escapes does it look like the fuel is boiling? I don't have a fix. We just slowly open the caps to release the pressure. Scary on a motorbike.
    #9
  10. [Art]

    [Art] Been here awhile

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    There were cases of the canister vent being not clipped back to the bash plate, and melting on the exhaust, hence blocking the whole system.

    See the FAQ for the pic of the evap system: https://790adventure.net/models/canister-vent/
    #10
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  11. BHoward

    BHoward Been here awhile Supporter

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    I own several KTM's, they all have done this to a certain extent. I have had the gas boil in my 1190, now that is scary to watch you bike shake around and hear the gas boiling inside.
    If you search the forms you will find many many instances of this very thing happening. Here's what myself and others have done to alleviate this problem which generally is caused by the fuel cap that has a very small vent hole which cannot accommodate the rapidly expanding gas in the tank.

    One of the best things you can do is take your gas cap apart and remove all check valves and bearings that stop the gas from spilling out in the case of a tip over. Or even better just by a C j's designs fuel cap that has a proper vent.
    Something else that possibly could help is line the inside of your fuel tank with heat barrier material. I have done this on my 1190 and transferred lessons learned from that bike over to my 790, lined the inside of the tank
    as well.
    #11
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  12. kubcat

    kubcat Long timer Supporter

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    Can you give me a link to purchase the heat barrier material? I'm about to pull my tank (again) to remove the Rottweiler dongle, and I would like to line the tank while I have it off. THx
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  13. windblown101

    windblown101 Long timer Supporter

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    Google amazon.com firewall heat barrier and you'll get plenty of options and various thicknesses. I bought a roll of 3mm thick heat barrier with an aluminum reflective side and adhesive on the other back when I had an 1190. Worked fine. I keep meaning to hunt up what's left of that roll for the next time I have the 790 tank off. Even though I've had zero issues since popping the check valves out of the OEM gas cap I figure reducing the heat in the tank is never a bad thing.
    #13
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  14. BHoward

    BHoward Been here awhile Supporter

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    #14
  15. kubcat

    kubcat Long timer Supporter

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    I'm getting the impression you think I'm down on Rottweiler... Not true, just the dongle that doesn't work as advertised. I'm pretty sure they sent the wrong one, since there was other stuff in the box that shouldn't have been in the order, including a large foam air filter that I don't recognize and looks like it belongs on a much larger engine. Hoping the airbox in plastic is available soon to upgrade the powerplate.
    #15
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  16. BHoward

    BHoward Been here awhile Supporter

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    Hey Kubcat, your a good sport.
    I'm sure if you call Rottweiler they will get you sorted out. I called them a couple days ago to order some extra filters for my power plate and they answered straight away.
    Seems the CF air box is a month out.
    #16
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