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912ULS Fuel Smell

in 912 / 914 Technical Questions 8 years ago
I am getting a fuel smell in my RV-12 primarily on climb out but also occasionally in cruise flight during turbulence. I am convinced that fuel tank has no leak. It might be carb float bowl overflow but I don’t see evidence of residue in the drip pans. Carb floats were weighed 8 months ago during condition inspection as follows – 6.1g (R) 6.2g (L). I’ve been using 93E10 for last 150 hours with no problems.

My question is… has anyone used a dye solution specifically made for detecting fuel leaks? I found a UV dye additive for auto fuel that fluoresces under black light. Anybody try anything like this?

  • Re: 912ULS Fuel Smell

    by » 8 years ago

    If you suspect something is overflowing while nose up, on the ground, try weighting the tail to cause the tail to touch the ground.
    Look for leaks and drips in this nose up position.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: 912ULS Fuel Smell

    by » 8 years ago

    Here are the most common causes of your fuel smell. Leaks can be small enough to be hard to find, but easy to smell.

    Float(s) have become heavy and are sinking causing the fuel to overflow into a vent tube. Even though you may not have fuel in the drip tray air flow can if the leak is small enough blow it out and or the heat from the exhaust help dry it up. They could have become heavy since your last weigh in inspection.

    The float level is not properly set on the float armature allowing the carb fuel level to become too high and overflow.

    The needle valve has a piece of dirt not allowing the needle to control fuel or it has a defect on the Viton surface.

    The carb float bowl gasket is starting to leak.

    The fuel pump is starting to leak out a weep hole (older AC pump) or the nipple on the newer Corona pump.

    If you have done any work on the fuel system recently start there.


    The RV12 should not be sensitive to fuselage pitch and make a carb leak.

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

    Thank you said by: David HEAL
      
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  • Re: 912ULS Fuel Smell

    by » 8 years ago

    In my RV-12 (with 912ULS), a slight whiff of fuel smell in the cockpit during climb-out typically means that I have a heavy pair of carb floats (> 7 ouns.). There may or may not be any sign of fuel residue (mogas w/ ethanol residue leaves an oily-like substance) in the carb trays. Roger's "things-to-look-for" above is great advice.

    ps -- Also, visually check your fuel line connections for weeping. I used Loctite 567 as sealant and it is working well with my mogas/10% ethanol fuel. Some classic aviation fuel sealants appear to breakdown when exposed to ethanol-laced fuel.
      
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  • Re: 912ULS Fuel Smell

    by » 8 years ago

    Roger

    Has Rotax come up with their new float design yet? I can't believe how expensive these little buggers are. Is 861-184 the correct part number for the latest release float design?

    Thanks...
      
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  • Re: 912ULS Fuel Smell

    by » 8 years ago

    All I can say that over the years there has been more than a one Mfg for the floats. Rotax is striving as we speak to make a better more dependable float. I have no other info so stay tuned.

    I will say this.
    Rotax has always been working in your best interest and tries to stay ahead of any issues. Some parts are Mfg'd by an outside vender and they have made mistakes. Rotax gets notified of this and jumps on it immediately to rectify any issues.

    This is no different than any auto, plane, boat or motorcycle, ect.. company. None of them make all their own parts and some are contracted out. If one of these outside vendors makes a mistake then the finial engine Mfg must jump in and fix it. Some companies are terrible about taking responsibility. Rotax has always jumped in and notified end users and worked to fix a problem they may not have made themselves.

    I'll take a company that does that any day over one like the car industry that weighs risk vs money and fails to fix something because they think it's cheaper to just fix a couple peoples auto over the 100K owners they should be working with.

    No one on this earth is perfect so I'm happy to have a company that has my back.

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

      
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