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912UL Engine vibration on throttle back

in 912 / 914 Technical Questions 12 years ago

  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    how does one check the carb piston slide? does the engine need to be running?


    Engine off. Take the top off the carb. It's a while since I've done it and I don't remember the details.
      
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  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    Hi Paul

    As Roger says, don't bury your head in the sand and convince yourself it is the engine.

    It could be a lot of other things, maybe the nose wheel, if you have one, spinning and being out of balance causing a low frequency vibration. This could be affected by prop wash and so only happens at certain times, and only in the air.

    Mark
      
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  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    Yep, won't bury my head, am open to all suggestions just need to go through each option one by one until problem solved. The reason I still think it is the motor/prop is that the engine mount tubes on the Skyranger are accesible in the cockpit to touch/feel. When the vibration occurs I can feel it though these tubes the most, the other cabin tubes not so.

    Cheers

    Paul
      
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  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    Paul Brydon wrote:[quote]
    how does one check the carb piston slide? does the engine need to be running?
    [/quote]

    Start by switching off the engine, removing the air filters and opening the throttle fully. Insert a finger into the venturi and push the piston up, release it and let it drop. There should be no resistance or delay either lifting or dropping. Both carbs should behave the same.

    Be careful, if you block the air holes in the bottom of the piston it will not move freely.

    You can also remove the piston from the top (only 2 screws to remove) and inspect it for scoring or rubbing.

    Hope that helps.

    With my own carb problem, I have now fitted the service kit to the carbs, so I have effectively replaced all the seals, diaphragms, needles and jets. I am hoping to go an try them out tomorrow.
      
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  • Re: 912UL Engine vibration on throttle back

    by » 12 years ago

    Start by switching off the engine, removing the air filters and opening the throttle fully. Insert a finger into the venturi and push the piston up, release it and let it drop. There should be no resistance or delay either lifting or dropping. Both carbs should behave the same.


    Ah, thanks for that. Learned something there. There's always an easy and a hard way. Most of the time I do it the hard way.
      
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