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Gas leaking from air filter

Discussion in 'The Garage' started by Bikebone, May 22, 2020.

  1. Bikebone

    Bikebone XS400 Member

    My son has a 1980 xs 400. He drove it to work today and ran it out of gas. While at work the left choke was left open. Late in the evening we fill the take and notices gas pouring out of the left air filter.
    Question: is this due to the choke being left open or possibly a float issue? Or some other issue?
     
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    Float valves or petcock not shutting off. The float valves are metering devises not shut off fuel valves. So make sure the petcock is shutting off first. If you are still using the stock one my guess is that.
     
  3. TOM SCHANNE

    TOM SCHANNE XS400 Member

    I was just going to post the same question. Upon turning on the fuel petcock, fuel started dripping out of the intake area of the left side air filter box. This happened a couple of times but not every time it was turned on. I tapped the carb bowl with the butt of a screwdriver and it stopped leaking so I'm assuming it's the float hanging up.
    I have a clear fuel line and filter so I can see that the petcock is shutting on and off the way it should.
    I'll take the carbs off and check the floats.

    What do I look for?
     
  4. Bikebone

    Bikebone XS400 Member

     
  5. Bikebone

    Bikebone XS400 Member

    Thanks for the insight. I'll start at the petcock.

    Just want to mention that when we first got the 1980 xs we rebuilt the petcock, approximately 3 years ago. There was a period after the petcock rebuild that the bike sat for 6 months. Is it common for the petcock to go bad within years, especially with today's gas containing %% of ethanol??

    Also still working on the 82 XS.
     
  6. xschris

    xschris a lifestyle not a trend Top Contributor

    The stock vacuum style ones are not very good to begin with. Today’s gas is another factor. Most of my bikes have non-vac ones now that you turn on and off. I also use Yamaha fuel med for ethanol fuel. Helps protect rubber and soft metal.
     
  7. TOM SCHANNE

    TOM SCHANNE XS400 Member

    Reading this has me a little confused.
    In regards to a non vacuum type, why would the petcock cause an issue with the gas flooding out the filter? Isn't the petcock just on or off (or reserve). I have an aftermarket non vacuum type, it doesn't sense when the bowl is full does it?
     
  8. xschris

    xschris a lifestyle not a trend Top Contributor

    Float valves are not fuel shut off valves just to keep a set amount in the bowls. If the peacock keeps letting fuel flow for long amounts of time or when it’s hot out the fuel can push past the float valves. Even more so if they are worn of not adjusted proper. Having a manual peacock stops the fuel once the bike is off after you turn it to off of course. Vacuum ones should do this after the vacuum from the motor has stopped but most of them the small o-ring in don’t make a good seal. Or the o-ring don’t have enough pressure to push it closed. When they work they are nice but they most often fail and have other leaks come from them. I only have one on all my bikes only because it’s a factory resto.
     
  9. TOM SCHANNE

    TOM SCHANNE XS400 Member

    So, on a non vacuum petcock, if fuel is dumping out the filter when the petcock is on, it's a float issue that needs to be fixed , correct?

    tia
     
  10. xschris

    xschris a lifestyle not a trend Top Contributor

    Unless the bike is running, the petcock should be off and fuel should not flow from it. If the petcock is on and the carbs over flow before you start it the float needles need to be adjusted or replaced. Good valves will stop the flow but you still need to have the petcock turn off fuel while the bike is parked. On his vacuum operated one when they go bad gas will still flow and can cause the float valves to leak and spill gas out of the carb. Float valves are not intended to be fuel shut offs from the tank but to only keep a determined amount of fuel in the carb while the motor is running. While the bike is running they will almost never fully close off to stop gas flow. Only to just stay open enough to keep the bowl full. They are a fuel metering devise. Most people think of them as a gas shut off when they are not. That's why all bikes have a petcock to turn gas on and off.
     

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