Stihl FS100RX trimmer leaking gas into air filter.

Discussion in 'Mechanic and Repair' started by G.M.Landscaping, Jun 2, 2012.

  1. G.M.Landscaping

    G.M.Landscaping LawnSite Senior Member
    Posts: 937

    My FS100RX is filling up the air filter with gas when not in use. Either in a horizontal or vertical position. I tried cleaning the carb a couple times with no luck. Instead of ordering a carb kit I ordered a new carb. It didn't come in yet, so I took a good working carb off of my FS90R and put it on till it comes in.

    Hung it up on my trimmer rack in the shed(engine up/trimmer head down). Now its doing the same thing. What's making two carbs do this? S88 & S131B carbs. It's definitely dripping out of the air filter assy. Gas cap and tank is dry.
     
  2. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    More then likely it's your tank vent, small black fitting on the top of your tank with a single hose that runs in to the back side of the air filter housing. Set it in the rack without the air filter and cover and keep your eye on the small hole in the lower left hand corner of the aluminum case.
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  3. Duekster

    Duekster LawnSite Fanatic
    from DFW, TX
    Posts: 7,961

    Floats could be stuck from old gas.
     
  4. G.M.Landscaping

    G.M.Landscaping LawnSite Senior Member
    Posts: 937

    Well I did that and that's where it's coming from. So I pop it out and it breaks. Guess it needed replaced anyways.

    Is this a valve that relieves pressure buildup in the tank?
     
  5. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    Nope one way valve to replace the used fuel from your tank with air, all fuel tanks are vented either by the cap vent or some kind of external vent. If not once the suction was too great it will slow or stop the flow of fuel and sometimes suck in the sides of some tanks.
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  6. ed2hess

    ed2hess LawnSite Fanatic
    Posts: 13,141

    So what happens on a hot day when pressure builds up in the tank?
     
  7. jtsnipe

    jtsnipe LawnSite Member
    Posts: 197

    Fuel injection.:hammerhead:
     
  8. G.M.Landscaping

    G.M.Landscaping LawnSite Senior Member
    Posts: 937

    So it's a one way valve that go from the filter housing to the tank. What happens if you plug the hose until the new part comes in?
     
  9. ed2hess

    ed2hess LawnSite Fanatic
    Posts: 13,141

    The 420 blower is exactly the same setup. I have never seen fuel come out of that tube but I sure know that a lot of pressure builds up in the tank on all three of my blowers.
     
  10. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    Thought I explained it pretty well, but your tank won't vent.....Stihl says that the lock cap with the orange center is also a vented cap I guess double redundancy.....
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