Both carbs on my Rotax 912ULS began to leak due to overfilling of the float bowls after only 95 Hobbs hours. The cause was permanent deformation of the Viton rubber tips on the needle valves. The deformation took the shape of the valve seat orifice and allowed the needle valves to seat almost 1/16 in. deeper in the valve housing. This allowed the fuel level to rise to the point that the bowls were overfilling. Bending the tabs on the float brackets didn't solve the problem. There was no damage to the valve seats in the carb body. New needle valves, float brackets, and gaskets solved my problem----temporarily---am I to expect to have to exercise the same cure after another 95 hours???? Lockwood Aviation Supply, Sebring, Fl. has some very convincing evidence (photos, etc.) that engine vibration can cause premature wear and failure of needle valves, float brackets, and other carb components.
  • Re: Bing Carburetor Flooding

    by » 11 years ago

    Hi Harold,

    Excessive vibration may upset the carb system. 95 hours is pretty rare. If Lockwood has evidence then there is another good arguement to keep the carbs synced at every100 hr. inspection and don't cruise or run for long periods in the mid to low 4000 rpm's. You should be cruising for extended periods over 5000 rpm. I keep finding way too many owners not keeping the carbs synced. It's easy to do and if you do it every 100 hrs. Is fairly quick. I just saw a plane for the first time the other day and the carbs were 6" of vacuum out. This kind of poor maint. Will take its toll on your engine in the long run.

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

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