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Thread: 912 flooded carb

  1. #1

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    Default 912 flooded carb

    Would like some advice. My right carb continued to flood out through the air tube with mechanical fuel pump at about 4#s. Put a pressure regulator on the gas line with a setting of 2#of pressure and bypassing the electric fuel pump. The pressure gauge when running shows 2.5 # and the flooding stops. The engine runs smooth at various rpms with run-up to 5000psi. Everything seems good. Question - is 2.5 lbs. of gas line pressure adequate for flight? If so, i will replumb through the electric fuel pump which i only use for takeoff and landing. Would appreciate your thoughts! thanks.

  2. #2
    Senior Member Delta Whisky's Avatar
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    Default Re: 912 flooded carb

    Taco - have you done anything to uncover the real source of the flooding? (Or, why isn't the float and valve doing its thing - properly?)

    Past that though, is 2.5lbs enough? That question is best answered by a fuel flow test. Can you run your system the way it is plumbed by the electric pump with the pressure regulator set to 2.5#s? With a pump system you need 125% of rated max power fuel flow. I forget the exact numbers for a ULS but it should turn out to be almost 10 gph.

  3. #3
    Super Moderator Av8r3400's Avatar
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    Default Re: 912 flooded carb

    I would consider at least replacing the needle valves, if not the floats, too. IMO 2.5 psi is not enough fuel pressure.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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  4. #4
    Senior Member 109JB's Avatar
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    Default Re: 912 flooded carb

    Well that all depends. There are many gravity feed systems that operate on less than 1 psi. Motorcycles, ATVs, lawn mowers, and airplanes come to mind. However, it depends on the carburetor and how it is designed to function. The Rotax 912 manual I have list fuel pressure limits from 2.2 to 5.8 psi, so 2.5 is in the green but at the low end. That said, 4 psi should not cause the carbs to overflow and there is something wrong. The carb floats on rotaxes are a know problem, and there is a test for weight of the float to determine if it is fuel soaked. Coincidentally the 582 uses the same floats as a 912 and I had a bad float on my 582 that caused the same issue. Replaced the float and all is good. Bottom line is you really need to find out what the real problem is, and 4 psi of fuel pressure is not the problem.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
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    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  5. #5

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    Default Re: 912 flooded carb

    Thanks for your thoughts! I think your right, there is a problem and regulating the psi to 2.5 really doesn't solve it. the floats are good so plan on mechanical sync to see if that helps and go from there. don't really want to take carb off but may have to replace needle. not mechanically inclined so all this is difficult. thanks.

  6. #6
    Super Moderator Av8r3400's Avatar
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    Default Re: 912 flooded carb

    What was the weight on the floats?

    Needles can be done with the carbs in place.

    Maybe you might consider having the carbs professionally gone through.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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  7. #7

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    Default Re: 912 flooded carb

    Quote Originally Posted by taco View Post
    Thanks for your thoughts! I think your right, there is a problem and regulating the psi to 2.5 really doesn't solve it. the floats are good so plan on mechanical sync to see if that helps and go from there. don't really want to take carb off but may have to replace needle. not mechanically inclined so all this is difficult. thanks.
    Did you weigh the floats?

    You can get one of these from Amazon for under $10.00

    Screen Shot 2022-07-03 at 4.49.38 PM.jpg

  8. #8
    Senior Member Slyfox's Avatar
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    Default Re: 912 flooded carb

    this kid has the same problem, right carb, left is ok. Now my plane is a 4 so the original left carb is now on the right. went 800 hrs with no problem, now the right one wants to flood and only when it's hot. I let things cool and turn on the facet pump and no leak. I fly for a half hour and taxi back to hangar and rough. stop and fuel is pouring out the vent of the right carb. I've rebuilt the carbs, replaced the floats (new), replaced the arm, replaced the needle, polished the seat. replaced the bowl with the updated one. I don't know what to do next other than replace the carb. Larry you say the needles with the red tip, you got a part number.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  9. #9

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    Default Re: 912 flooded carb

    yes, i weighed the floats and under 7oz. I've read it's really difficult to replace needle valves with the carb in place, is there a simple way to do it? first i am going to resynch the carbs both mechanically and pneumatic. dont know if vibration problem causing overflow? thanks.

  10. #10
    Senior Member Slyfox's Avatar
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    Default Re: 912 flooded carb

    Taco, first off mine would leak with engine off. Now I replaced my original needle and arm because I would get a little fuel on the floor about the size of my hand when I came into the hangar with the fuel on. So a long while back I started turning the fuel off after flight. I changed out the needle and arm and started having flooding problems. Now with that said the definition for NEW is = never ever worked. So I just went out to the hangar and put the old needle and arm back in, I run the facet pump and flushed the needle real good and made sure it was centered good. I put things back together and ran it, ran great, and warmed it up good. no leak so far. I put things back together and am now waiting for good weather, high winds right now and thunder storms coming through. will see how things work out.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

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