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Gas vapor issue

Discussion in 'XJ Technical Chat' started by MrSeca, Aug 27, 2020.

  1. MrSeca

    MrSeca Active Member

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    Need help guys. As I understand it, the gas caps on these XJ's are vented so as to allow the gas to flow freely through the petcock and into the carbs. Unfortunately, when it is extremely hot the gas inside the tank starts to expand and gas vapor escapes through the vent and you can constantly smell it. It just so happens that I park my bike next to my window and the vapor flows into my room causing my room to smell like gas. Does anybody have a remedy to this situation?
     
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Park somewhere else.
    Really.
    The gas cap has to vent or bad things will happen.
     
  3. raskal

    raskal Active Member

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    I haven't laughed a lot in 2020, but that was good one
     
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  4. MrSeca

    MrSeca Active Member

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    Can it be sealed when parked only?
     
  5. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Does it stop being hot outside when you park?

    The vent has to remain free to do its job.
     
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  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    is it just the heat or do you park in the sun?
    cover tank with a light color cloth when parked.
    wet it down and the evaporation will help keep it cool untill it dry.
    maybe you need to replace the seal on the cap or you have a good nose.
     
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  7. MrSeca

    MrSeca Active Member

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    It's mainly the heat. The bike is in my driveway. I have a motorcycle cover over the bike and also a canopy covering both of my bikes. Truth be told it does not annoy me that I smell gas. You actually only smell it when I drive away or when I park. However, it's my roommate whose day I ruin because she's more sensitive to it. Since I wrench on bikes I barely notice it. The only solutions it seems is to park on the street. I understand it's a rather unique situation and I was hoping I could find some alternative so I can continue to enjoy the benefits of parking in my driveway. We also have alternate side parking on Monday and Friday so if I park on the street that would mean relocating 3 vehicles twice a week!
     
  8. Polock

    Polock Well-Known Member

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    try closing the gas cap on a baggie. but that may force gas through the petcock and into the carbs, that might be a problem or not
    get a pet skunk
     
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  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    maybe you are running rich, if it is only when drive away or park.
    roll it down the drive before starting.
    My wife has a good nose for fuel smell, a few adjustments much of the smell went away.
     
  10. JCH

    JCH Active Member

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    I don't believe that sealing the cap is a good ideal,it may cause too much pressure in the float bowls and then dump fuel into the air filter box and engine.
     
  11. XJ550H

    XJ550H Well-Known Member Premium Member

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    the float bowls are vented, the holes in the throat on airbox side go into the float bowls. there is a name for the purpose that eludes me at this time.
    it is some sort of balancer thing. gives the air in bowls someplace to go when fuel is entering bowls. hatachi and mikuni have them . on mikuni (550) only 1 is a vent the other is an air jet.

    this feature may also be why there is a fuel smell. fuel in bowls eveporates and goes out the air box intake port, draining fuel line when needles open to compensate for fuel level droping.
     
    Last edited: Aug 28, 2020
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  12. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    I doubt if it’s from the carbs (unless your find it dripping).......he’s right—the cap is SUPPOSED to vent. If it vents and you’re near enough, you’re GONNA smell it. The only logical solution is to PARK SOMEWHERE ELSE as others said
     
  13. cgutz

    cgutz Well-Known Member

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    I park mine in a garage next to a window that is always open, with a window fan as an exhaust. After a hard run, the hot engine causes fumes through the gas cap until the engine and tank cool down.
     
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  14. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    I'm not buying it's ONLY gas vapor venting from the tank. Or carbs via their vents. There is another issue somewhere; either a balky float or seeping petcock/weepy float combo. Are you monitoring your engine oil level to ensure it isn't increasing as gas becomes added to the oil? A persistent strong gasoline odor indicates it's escaping somewhere in liquid form. It may not be externally immediately noticeable, but liquid gas is getting somewhere it's not supposed to be; normal evaporative emissions are doubtful the cause. I have a tiny garage, and while I try to let the bike cool down prior to pulling it in, it often gets garaged warm; and it only ever smells like "warm motor" there is no distinct gasoline smell. The only time I've had actual gasoline odor was when my petcock decided to pack it in during winter storage and a balky float or two contributed to gas to begin draining into the motor. No outward puddles but it sure stunk.

    I would start by checking the petcock to be sure there is no fuel flow/drippage without vacuum when in ON or RES. And monitor your engine oil level for a sudden increase.
     
  15. MrSeca

    MrSeca Active Member

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    Bigfitz, you are correct. Leaky petcock. I should've known. I was kind of in denial because I don't want to work on bikes anymore. Ugh! I also have a gas leak out of the overflow tube on the #4 Carburetor. However, it only leaks when the engine is turned on. If the bike is parked and I switch the petcock to PRI there is no leak out of the overflow tube. I checked the float bowl level using the clear tube method and the gas comes right to the lip of the float bowl carb just above the screws so I'm pretty sure that's correct. Anyway, I'm also not exactly sure if the two issues are related or not.
     
  16. JCH

    JCH Active Member

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    That level seems high to me,did you say what year your bike was,i never leave it on prime,but if your petcock is leaking i suppose it doesn't matter.
     
  17. MrSeca

    MrSeca Active Member

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    This is an xj900 Seca
     
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  18. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    If you don't want to work on bikes anymore, owning a 38-year old motorcycle is not the way to go.

    Virtually all new street bikes are fuel injected; and the new Royal Enfield 650s have a three-year unlimited mileage warranty. So for a mere $6000 or so, you wouldn't have to work on bikes anymore. At least not as much.

    It's an unfortunate fact of life that '80s era bikes are simply going to take some working on. In your case, the issue with #4 sounds like the float level is simply too high; and of course you know about your petcock.
     
  19. MrSeca

    MrSeca Active Member

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    I do want to work on bikes. I'm just a little burned out. I started about 3 years ago and it just never ends. Nevertheless, I hear what you're saying.
     
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  20. biggs500

    biggs500 Active Member

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    The good news is petcocks are easy to rebuild. I think Fitz did a write up a few years ago. And the 900 you have is super rare!
     
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