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Hi all,

 

Quick question, what is the clear carb overflow tube made of?

Tygon, polyurethane, pvc, etc...

I'm making a cold air intake and need to extend these tubes so they are getting the same pressure as the incoming air.

 

Thanks!

  • Re: Carb overflow tube material

    by » 5 months ago


    The Carb "Overflow" Tubes are actually Float Bowl "Vent" tubes used to equalize the pressure in the Float Bowls to match the pressure at the Carb Throats.
    They exist to allow a connection to aircraft with airboxes and Carb heat.
    Otherwise, they are just short hoses terminated in the vicinity of the Air filters in most aircraft.

    They will never experience liquid fuel under normal operating conditions.
    Flooded Float bowls will overflow into the carb throat through the fuel jets long before the "Overflow" Tubes get wet.
    Any material compatible with fuel vapors will be acceptable.
    PVC (Vinyl) tubing will get stiff over time but as long as it is still flexible enough that it doesn't crack when flexed, it is still usable in the vent-to-nowhere application.
    Tygon or similar would be recommended if attaching to an actual airbox.

    DO NOT Ever think that running these hoses to the bottom of the engine compartment so they dump overboard is ever a good idea!!!


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.


  • Re: Carb overflow tube material

    by » 5 months ago


    The clear "overflow tube" (Actually a Float Bowl Vent Line) MUST remain in a natural pressure zone (Very important!!!). This tube is placed between the float bowl and the spring clip because that is (in general) a neutral pressure zone. If the engine comes equipped with a Rotax airbox, the tube is attached to the nipple fitting on the airbox (neutral pressure zone).

    The P/N for the 120mm vent line tube is 256 035 (under float bowl spring)

    The P/N for the vent line tube (HOSE 4x7, IN A ROLL, 200 MM) that attaches to the Rotax airbox is 860 660

    We can't stress enough how important it is for the float bowl vent line to remain in a neutral pressure zone, Please watch this video for more information:  https://www.rotax-owner.com/en/videos-topmenu/rotax-minute/454-carb-vent-lines


  • Re: Carb overflow tube material

    by » 5 months ago


    Thx bill and moderator,

    I made a cold air intake and need to extend these lines so they are at the same pressure as incoming air.

    I can not leave then under the carb bowl bail just like anyone who has the rotax airbox can not leave under bail.

     

    Tygon better than polyurethane?

    I just read pvc hose has 150f temp range wich I don't like.

     

    Thanks!

     

     


  • Re: Carb overflow tube material

    by » 5 months ago


    I’ve used both for 15 years and have never had an issue. I’ve used both and seen both used for fuel and after 3 years in service no issues. Flight Design uses both.


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


  • Re: Carb overflow tube material

    by » 5 months ago


    Whichever material you choose I suggest that you put some sample pieces in a jar with the fuel you typically use. It is very instructive to see how differently the various materials react to different fuels over time. 


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