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FYI: I replaced all four of my factory-original carb floats with new-style/dimpled floats back in June 2015 (172 hrs. TT HOBBS) in accordance with SB 912-065UL (R3). When first installed (dry and fresh from the package), the new-style/dimpled floats weighed @ 2.8 grams each.

During my recent Condition Inspection (298 hrs. TT HOBBS), my four new-style/dimpled floats weighed as follows:

Right carb @ 3.4g + 4.4g = 7.8g (i.e., over the 7.0g SB limit)
Left carb @ 3.2g + 3.1g = 6.3g (i.e., getting close to the 7.0g SB limit)

It appears that ROTAX may still have sinking float issues with new-style/dimpled floats. According to my ROTAX Service Center (CPS), ROTAX is not offering warranty replacement consideration on the new-style/dimpled floats.

Very frustrating! :angry:
  • Re: Sinking New-Style Carb Floats

    by » 8 years ago


    Yeah, I had a similar problem. I replaced my old style floats with the new ones before first engine start. Had one of the new floats sink at about 25 hours and replaced it. All still OK now at 100 hours.

  • Re: Sinking New-Style Carb Floats

    by » 8 years ago


    It is possible a float can still sink. That has been that way since the beginning. The 6.3 floats are fine and may never change. Replace the heavy ones. The new testing procedure is 99%, but there is still a 1% chance and nothing is 100%. The new inspection update mandates all floats now be checked at the 100 hr. or annual inspection. You were supposed to check float bowls here anyway so now just drop the floats on a scale. If your floats are good for a period of time there is a great chance they may last for years and or TBO.

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


  • Re: Sinking New-Style Carb Floats

    by » 8 years ago


    Thanks Roger for the reply. It just really irritates me that the customer once again has to perform and pay dearly for ROTAX's apparent absence of effective factory quality control (e.g., continuing to produce and sell floats that absorb fuel). When a new carb float prematurely fails, that is a factory defect! ROTAX should quickly replace the factory defective float at no cost to the customer. Rant over -- have a nice day! :woohoo:

  • Re: Sinking New-Style Carb Floats

    by » 8 years ago


    Rotax doesn't make the floats. They are made for Bing that puts them in the carbs. Many floats go to TBO without any issues. Rotax has MFG 45K engines with millions of run hours and most floats have been just fine. The US has about 20% of the engines. Floats can go bad and that is the same in many carbs with floats. If you get a new float and it sinks fairly quickly call your service center. Bing never thought there was an issue with the floats. It was Rotax that pushed the issue to have better testing before installation. The proper place to vent would be at Bing.

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


  • Re: Sinking New-Style Carb Floats

    by » 8 years ago


    David, I think you should ask CPS to make a warranty claim for you. second time lucky?

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