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new carbs venting fuel at 2500rpm and below

in 912 / 914 Technical Questions 12 years ago

  • Re: new carbs venting fuel at 2500rpm and below

    by » 12 years ago

    Don,

    Just went out and checked my floats and they float with the pins right at the fuel level. I lift them out and the fuel level is about 1/2" from the top of the bowl. I believe Roger is right. It doesn't sound like a float problem.

    If you are venting down toward the ground you might try looping the vent line up a couple of inches above the vent barb in the carb before going down with the vent tube. Sort of like a drip loop in reverse. I know of a couple of installations where the vent line runs uphill and into the air filter. This might stop fuel from splashing out of an otherwise healthy carb.

    Bill.
    Thank you said by: Don Hudgeon
      
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  • Re: new carbs venting fuel at 2500rpm and below

    by » 12 years ago

    Hi Don

    I have just been reading your post and I see you have cleaned your carbs with carb cleaner and compressed air. There is a good chance that you have dislodged or possibly damaged one or both of the diaphragms with the air. I would suggest you take the top of the carb off and check there are no tears. when you replace it just make sure the notch lines up. It will only take 5 mins to do both and I recon it will solve your problem. I am speaking from experience.

    Cheers Mark
      
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  • Re: new carbs venting fuel at 2500rpm and below

    by » 12 years ago

    Hi Roger,Bill and Mark.
    My new floats arrived this morning. When I installed them I made note of the "float-ability" of the originals and compared to my new (very expensive)ones from Rotax. From what I observed they appeared to be exactly the same. (Bummer). Anyway I thought I might as well try a startup and see what happens.Just in case there was no improvement, I added 2, 8 inch vent tubes and ran them into containers attached to the engine mount.I also left the fuel shut off.
    The engine started immediately and ran smoothly just like it always has. No fuel spitting,no shaking. I warmed it up, reconnected the vents to the air filters and synced the carbs. They were right on!!
    I ground checked everything at all rpms and prop pitches. Fueled up and flew for an hour. Just did circuits until I regained confidence in the performance before venturing over hostile terrain. It is pretty much ALL hostile where I live.Lots of mountains bush and lakes.
    I have no idea why this has happened. The only thing I can think of is maybe these old floats become porous and loose their buoyancy,or maybe as Roger said there was a speck of contamination. I did not remove anything other than the carb bowls this morning.
    It runs very well now, maybe after 17 years or so Rotax requires a certain amount of money to be spent and I was not there yet!!!
    Thanks for your help everyone. I sure hope I had a better "smoking gun"
    Cheers
    Don

    PS. Mark, when I cleaned the carbs, I had the diaphram and needle valve removed.
      
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  • Re: new carbs venting fuel at 2500rpm and below

    by » 12 years ago

    Hello everyone. I had an interesting occurrence a few minutes ago that is very similar to what is described here. Just after take off I smelled a strong odor of fuel. A quick landing and shut down revealed fuel over boarding from the left carb. When I removed the bowl for inspection I discovered the floats had "flakes" coming off them with a few lying in the bottom of the bowl. The engine is approximately 5 years old with 171 hours. Has anyone seen this before where the floats begin to crack and flake? This engine has always been fueled with premium unleaded.

    Thanks,
    Jay
      
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  • Re: new carbs venting fuel at 2500rpm and below

    by » 12 years ago

    Hi Joseph,

    Yes flaking does happen, but not real often. If yours are flaking then you will need to replace them.

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

      
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