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Hi all, I am new in this forum, I have a very short experience as pilot (350 hrs)

I fly here in Eyrope an Eurostar with 912ULS, 100hp with airbox.
In winter foggy days, I usually fly in the sunny Alps between 10000 and 14000 feet, usually 2 hrs flight lenght.
I check fuel tank and filter for water before every flight (never found); I refuel with water filter, I cover half of the radiator with tape.
In the long descent I usualy pull carb heat, trying to keep CHT and oil around 70° C

In the first 100 hrs service, the mechanic here (rotax certified) find 1 spoon of water in both carb sinks: nothing in the fuel filter, nothing in the tank.
He said: “ you fly in winter, you have condensation inside the airbox that goes inside carbs...the solution is to put a temp sensor inside the aibox, and when you go below 18°C , pull carb heat no matter if you are climbing or level”
And so we did, but at 200 hrs service I still had water (1 tea spoon), I use more carb heat and at 300hrs service I still have water (1 tea spoon)
When I pull carb heat I have an evident power decrease, not nice to feel when in the mountains...
Any suggestion?
Do I have to empty carb sink more frequently?
Is the carb heat an “all or nothing” control as the manuals tells,or I can use it also gradually, just to keep my right temp in the airbox?
thanks
  • Re: water in carburetor sinks

    by » 12 years ago


    You mentioned a fuel filter. Is this a true fuel filter or is this a gascolator / water separator? If all you have is a fuel filter then that isn't good enough. I don't believe this is an airbox issue. Do you have a low point in the fuel system to check for water before each flight?
    At 10K-14K ft. the air is usually cold and drier, agreed moisture can certainly be there. The air through the air intake goes through the carb throat and is either burned through with the fuel or can collect and cause carb ice under the right conditions, but this moisture doesn't flow backwards into the carb bowl. Fuel is coming up from the carb bowl and into the throat of the carb. I can't see how any moisture could flow backward. Using the carb heat will get rid of carb ice and it then just passes through the system, but carb heat won't get rid of water in the carb bowls.
    The carb bowl water usually comes from the fuel. Is this fuel 100LL or auto fuel and does it have any alcohol? The water in the carb bowls comes from the fuel traveling through it. You need to have a water separator on a low point in the fuel system. I would take a hard look at what's in the fuel to start with. If you are using 100LL then the water is probably at the bottom of the fuel from your source and should be drained. Not using the fuel off the very bottom of a system and up a little higher in a tank will help keep low settling water out. Try a different fuel source for a while.

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


    Thank you said by: alessandro pezzola

  • Re: water in carburetor sinks

    by » 12 years ago


    Roger, thanks for your answe... moves me back to a fuel problem...
    to answer to your questions:
    1) it's a fuel filter, not a gascolator
    2) I dont have any low drain point between tanks and carbs
    3) I use mogas, not added with alcohol
    4) each tank has a 1 liter sink where water is supposed to lay, and I check before every flight.
    I always use water separetor at every refuelling

    If I understand corrctly, you suggest to:

    1)install a water separator on a low point in the fuel system
    2)stop to use carb heat even when I read low temps in the airbox (unless dew point suggest icing possible)
    3)check for better quality of gas

  • Re: water in carburetor sinks

    by » 12 years ago


    Yes to your 3 questions.
    The carb heat won't help what's in the carb bowl, but certainly use it if you think you have carb ice. I believe a water separator at a very low point in the fuel system would help you and yes, try another fuel source for a while and see what happens. If you are using a Mr.Funnel that supposedly separates all the water from fuel, well I'm not a big fan after I did some testing. I don't think it does what it claims.

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


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