On the bottom of the Rotax airbox on my engine are two hoses (one on each side) that are routed to the bottom of the engine side of the firewall as a drain (?). Since new there has been some drainage mainly on the pilot side. Questions are:

1. Is it a normal finding to have drainage coming from these hoses.

2. If not, how do you fix it?

There are some yellow stains on the bottom of the plane and I believe that it is unburned gas coming from these hoses.


  • Re: Rotax 912 Airbox drain(s)

    by » 13 years ago

    Hi Duane,

    These are vent tubes, but fuel can puke out the tubes. Yes they could have some raw fuel coming out or even condensation if you live in a humid climate and the conditions are just right. The fuel may be coming out because the carbs are out of balance and they need to be synced (usual cause). It could be bad engine mounts or a prop out of balance which causes the engine to shake and then the floats in the carbs can't control the fuel very well and they vent fuel. First thing is to sync the carbs.
    If the above items fail then you may need to pull the carbs and re-adjust the carb floats, but this is usually a last resort.

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

  • Re: Rotax 912 Airbox drain(s)

    by » 13 years ago


    Thanks for the information. At 200 hours (now have 275) I had the carb sync checked. It was spot on. Also, my EGT temps are usually no more than 30 degrees F apart. I am not so much concerned that there is some gas getting on the plane, but don't want any fire danger. The good thing is that the drain tube is downstream from the exhaust. Next time it is in for service, I will have the carbs looked at.

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