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Fuel venting/dripping out air filter/intakes 912S

in General Tech Discussion 10 years ago

  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Shaking carbs was a first thought but the carbs are synched with new carb sockets and the engine was running really smooth. We are noticing it with another 912S trike but the gas is strayed back in the airstream and it is not noticed as much. Perhaps it is the altitude since we are flying out of a 4700 foot airport. I installed an airbox and this has solved the problem for me but I am still wondering about this Rotax problem......
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Food for thought with a few ideas,


    Most Rotax carbs or engines don't puke fuel. If anyone's Rotax does then you just haven't found the problem.
    I would say for those that do it may be a bad needle valve (pressure test needed), carb vent tube located in the wrong place causing issues with in the carb bowl, poorly synced carbs, bad engine mounts(any (caused from any engine vibration whether you know it's there or not)(either old or poorly conceived from the factory) (Kitfox had this very issue with engine mounts), bad carb bowl gaskets, Prop so far out of balance it shakes the engine, leaks at the fuel line attachment on the side of the carb which is hard to find on an exposed engine, old dry rubber carb intake sockets, a small leak may occur on the carb body where holes were drilled during MFG and the little ball bearings were inserted later and covered with epoxy, (these may need a new coat of epoxy),it is possible, but I don't know how likely an odd type of air filter may lend itself to this???
    Possibly a leaky air intake valve allowing exhaust pressure to escape and blow back out the intake?

    If adding an airbox cured your issues then an air flow issue some where seems like a likely cause. Is it possible your carbs still puke fuel, but is contained and pulled back into the carbs?

    Altitude shouldn't have any affect on the fuel puking from the carbs. People fly out of sea level and up out of 9K+ air fields without any issues.

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

      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Well i just heard of the same problem with someone operating at a base airport of 7200 feet msl. This confirms my theory of high altitude operation since it is only happening with 912s at high altitudes. I ended up changing from an airbox to two seperate air ducts to air filters. This has completly solved the problem as i have posted on this forum earlier.

    My other high altitude flyer is going to go with some setup that will lean the carbs at high altitude. Hopefully this will be another fix and provide better power. We shall see.
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Hi Paul,

    If you live and fly most of the time at high altitudes like your 7200' you can drop the needle clip one notch without any issues and as far as the fuel drip I would make sure your float level is properly set. This would be more likely the common cause. It should be leaking fuel unless the float height is off or a float is sinking and it can't control the level in the bowl. It could also be affected by where the carb vent tube is placed. I dozens or people that fly out of 7100' elevation airports and fly from 10K-13K all the time. They have no issues. They have outside air inlets and airboxes.
    I thinking swapping your setup might just be a band-aid to another problem.

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

      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Yes the first thing a did was check the float levels. Than I replaced the needle valve, did the pressure check, even replaced the carb with a perfectly good one that was having no problems on another aircraft and it did the same thing, spewing fuel out the air filter. When I installed an airbox the problem went away. Yes an airbox solves the problem. so I installed separate airducts about 18 inches to the airfilters and the problem is also solved. I understand that operating with an airbox does not have this problem but operating WITHOUT an airbox at high altitudes does.
      
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