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Fuel venting/dripping out air filter/intakes 912S

in General Tech Discussion 11 years ago

  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    I have a 912ULS in pusher configuration (flexwing microlight) and last flew 31st Dec. The engine was difficult to start (ended up jump starting it after flatened battery), then I noticed some loss of power when throttling back to 3000rpm at about 3000ft near clouds. Recovered after throttling up, and selecting mixture to rich ("reduces pressure to the float chambers by piping partial carb venturi pressure..")

    Mentally put it down to possibly icing, but never had before, so didn't really believe it!

    Went to fly again yesterday, first time since December. Engine again difficult to start, and was very lumpy, wouldn't idle, etc. Also... fuel dripping steadily out of air filters. Too close to the hot exhausts for comfort (being a pusher the airflow was from the filters back over the engine).

    Anyway, took filters off and could see carbs very unbalanced. Mechanically balanced them (by visually comparing sync position of carb piston lift - one advantage of having the engine right behind your seat!), and fuel drip problem appears solved. At least when engine is hot - proof will be next time I start it from cold.

    However engine still won't run cleanly on 'Lean' at less than full throttle so something else amiss. Trying to think how that mixture control works in practice... and whether reducing the pressure in the float chambers will in some way cause problems with the levels, etc.

    Again, it has worked OK in the past so something has changed, perhaps a blockage in the constriction valve, or similar. I'll give it a good blow through.

    Any other ideas?

    Best, Peter
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Hi peter,

    Looks like it may be time to pull the carbs and clean them. How many hours on the engine and how long has it sat without flying? You may have some dried fuel clogging or just some debris and you can't totally rule out a bad float. You can weigh them to check. They should not be over 7 grams when weighed together as a pair.

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

      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Roger,

    Thanks for the reply.

    The engine has just over 1000 hours, I gave it a 200/500 hour service, including carb dismantle and clean, rubber diaphragm checks, needle wear visual, etc. early 2014, and thereafter flew some 50 hours last year with no hint of problem.

    I checked the bowls/floats early December 2014 as part of my annual maintenance. All looked good (the floats floated! but admit not weighed) but it seems I may well have disturbed something at that time.

    I think I must schedule in a day for some serious TLC before next going flying. I'll post if I find anything unusual.

    Regards,
    Peter
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    With a 1000 hours it would be a good time to do a carb rebuild.

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

      
    Report

  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Hi
    My 80 hp has more than 1100 hours and i have also got problems with fuel dripping out to the air filter, but only when the engine is not running. The dropping starts about one hour after engine is shut down.

    When i start the engine the dropping stops instantly. So no problems during flight. Have tried with new float needle without solving the problem.

    My solution is to shut off the main fuel valve after engine is shut off (after landing). I am going to buy a new pair of carbs when the problem with the carb floats is solved by Rotax/Bing. Does anyone know when that problem is solved???
      
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