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fuel dripping from air cleaner

in 912 / 914 Technical Questions 11 years ago
I'm just in the beginning stages of running this used 912uls and I'm getting a small amount of gas and air filter oil dripping from the air cleaners and running down the firewall. These carbs were overhauled by LEAF during a pre buy inspection so I'm doubting it's an adjustment problem. The engine runs smooth throughout its range. The carbs were synced with a twin engine manifold gauge. After speaking with a rotax mechanic I't was suggested that the muffler is possibly to blame having to much back pressure for the engine and actually blowing air & gas out of the carbs.
This is installed in an Avid Flyer and uses a muffler thats approx. 4" in diameter. Any ideas on this?

Travis

  • Re: fuel dripping from air cleaner

    by » 11 years ago

    If engine runs ok throughout it's range, I don't think it's a backpressure issue. If you had sufficient backpressure to throw fuel out of carb, engine would run poorly if at all.
    As you had carbs rebuilt, I'd look for float level being too low, allowing fuel to continuously feed into carb. Float arms should be parallel to housing when full up. This is assuming you don't have some weird installation with engine tilted severely. Also check floats to make sure they are not binding.
    Bob H
      
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  • Re: fuel dripping from air cleaner

    by » 11 years ago

    Does fuel also leak from vent lines? A carb overhaul does not include the float valve seats and I found that new float valves doesn't always fix a leaking overfilling bowl. I replaced the seats in mine and now the carbs seal.
      
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  • Re: fuel dripping from air cleaner

    by » 11 years ago

    Had the same issue, turned out to be bad floats. The old floats were saturated with fuel. Only had about 40 hours on the engine at the time.
      
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  • Re: fuel dripping from air cleaner

    by » 11 years ago

    I see they just released a SB for any floats manufactured since june 2012 that they may leak and have to be checked every 25hr or 60days till they sort out a different design..
    I don't get that at all. I just bought four new floats at over $200 and now i have to check them every 25hrs because they might be faulty? I wish i knew the whole story
      
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  • Re: fuel dripping from air cleaner

    by » 11 years ago

    Hi Scott,

    Not every float is bad or will sink. It is a warning to just keep an eye out. If you just bought new floats you may not even be affected.

    I wouldn't overly worry because if a float sinks you should have some symptoms.
    If a float sinks the fuel level won't be controlled and it will flood the carb. This should show up as fuel venting from the vent tube, you may have some dripping from an air filter depending on how your system is configured, many have fuel smells in the cockpit if you have a tractor prop (not a pusher) and the engine usually runs a little rougher. You may have a cooler EGT on one side because of some flooding. A quick look at a carb sync may be way out. They only take a few minutes to check. I quick easy way to take a look is to loosen the rubber carb flange clamp. Push the carb straight back out of its socket and lift it up about 2". Then just use a screwdriver to pop the bowl off. If a float has sunk the brass pin will be under the level of the fuel and the two floats in that bowl will not be at the same level. One will be under the fuel level.
    I have had 1-2 of these and the first thing the customer said was he smelled fuel and had some rough running. When the cowl was off his plane and it was running you could see the fuel puking out the vent tube.

    Just a couple of quick ideas to help trouble shoot.

    You can as the SB says to weigh them too. I haven't had to ever go that far.

    The 1-2 I saw happened within 100 hrs of being a new engine. One was only 60 hrs. on an RV12.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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