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Thread: engine runs rough

  1. #21

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    Default Re: engine runs rough

    May have mentioned this before, when balancing carbs I do idle and cruise power settings and then check mid range, the twin throttle cables are the best the springs are not as strong going too full throttle, but are very necessary, if you look at the arm as it travels from closed too full throttle it goes in a slight arc, if there’s any lack of smoothness they lag thus imbalance. With the electronic carb mate balancer you can see if this is occurring, remember throttle must be closed when using choke for start,
    If you open the throttle even a quarter the choke become ineffective. Always check the springs are secure on that choke as well.
    there’s no voodoo in balancing the carbs, if you want too change the idle , turn both idle stop screws the same amount, please stop the engine before adjusting anything, one slip or lack of consideration of what that whirling prop will do is not worth the cost.props are live always! treat so,
    even with those mags off!
    That’s why a dead cut check during shut down confirms the sucker is grounded,
    stay safe,

  2. #22
    Senior Member Slyfox's Avatar
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    Dec 2008
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    felts field, spokane
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    Default Re: engine runs rough

    Quote Originally Posted by sturdee View Post
    May have mentioned this before, when balancing carbs I do idle and cruise power settings and then check mid range, the twin throttle cables are the best the springs are not as strong going too full throttle, but are very necessary, if you look at the arm as it travels from closed too full throttle it goes in a slight arc, if there’s any lack of smoothness they lag thus imbalance. With the electronic carb mate balancer you can see if this is occurring, remember throttle must be closed when using choke for start,
    If you open the throttle even a quarter the choke become ineffective. Always check the springs are secure on that choke as well.
    there’s no voodoo in balancing the carbs, if you want too change the idle , turn both idle stop screws the same amount, please stop the engine before adjusting anything, one slip or lack of consideration of what that whirling prop will do is not worth the cost.props are live always! treat so,
    even with those mags off!
    That’s why a dead cut check during shut down confirms the sucker is grounded,
    stay safe,
    yup agree with all that. I was thinking of the springs as well. I was considering ordering the spring set up that vans has for the rv12 with the 912uls. thanks
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  3. #23
    Super Moderator Av8r3400's Avatar
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    Default Re: engine runs rough

    Steve - Did you try new spark plug wires or boots? ( got mine from the local fleet-farm store in the snowmobile parts aisle)

    Also, I have found gapping the plugs to .021-.022" (.53-.56mm) is far better running than the Rotax spec.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  4. #24

    Default Re: engine runs rough

    If you’re getting rough vibrations as you pull out power I am going to go out in a limb and ask you if you’d mind tinkering with your idle fuel screws a bit. Try setting them to 1/2 to 3/4 turns out from fully seated and do a full power run up before flight. If all goes well in run up, lap in the pattern and on the decel on downwind note if the vibrations improve or get worse. If they improve, your needle circuit and idle circuit may be wayyyy too rich a I’ve seen most people report. That idle fuel screw is a quick means to diagnose.

  5. #25
    Senior Member Slyfox's Avatar
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    Default Re: engine runs rough

    Quote Originally Posted by AvDES LLC View Post
    If you’re getting rough vibrations as you pull out power I am going to go out in a limb and ask you if you’d mind tinkering with your idle fuel screws a bit. Try setting them to 1/2 to 3/4 turns out from fully seated and do a full power run up before flight. If all goes well in run up, lap in the pattern and on the decel on downwind note if the vibrations improve or get worse. If they improve, your needle circuit and idle circuit may be wayyyy too rich a I’ve seen most people report. That idle fuel screw is a quick means to diagnose.
    this is with idle mixture at 1/2 out. was going to try 1 turn out.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  6. #26
    Senior Member Slyfox's Avatar
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    Default Re: engine runs rough

    going out on a limb. has anybody had the guts of your exhaust fail. meaning did it come apart. I was thinking of pulling the muffler and looking inside
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  7. #27

    Default Re: engine runs rough

    Quote Originally Posted by Slyfox View Post
    this is with idle mixture at 1/2 out. was going to try 1 turn out.
    you planning to attend the KF factory fly in? I may be bringing the dual monitoring exhaust setup I made to display and we can strap it in and ground run it to see where you’re at.

  8. #28
    Super Moderator Av8r3400's Avatar
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    Default Re: engine runs rough

    Quote Originally Posted by Slyfox View Post
    going out on a limb. has anybody had the guts of your exhaust fail. meaning did it come apart. I was thinking of pulling the muffler and looking inside

    I’ve had two fall apart. The blast tube rots away leaving the stinger unsupported then the housing cracks.

    I usually smack the stinger on preflight and listen for a rattle to tell…

    I have one on my workbench to rebuild right now. Will make a new blast tube and retrofit ball and socket joints to hopefully make it my last exhaust system.
    Last edited by Av8r3400; 06-14-2022 at 09:39 AM.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  9. #29
    Senior Member Slyfox's Avatar
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    Default Re: engine runs rough

    Quote Originally Posted by Av8r3400 View Post
    I’ve had two fall apart. The blast tube rots away leaving the stinger unsupported then the housing cracks.

    I usually smack the stinger on preflight and listen for a rattle to tell…

    I have one on my workbench to rebuild right now. Will make a new blast tube and retrofit ball and socket joints to hopefully make it my last exhaust system.
    thanks Larry, I had one do similar on my io360, ended up cutting out all the baffles inside for both mufflers and made them straight pipe. I also thought of banging on the muffler real quick, but I think I'll pull the muffler and take a look. On the outside it looks great. I do understand the rotax needs back pressure, correct me if I'm wrong.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  10. #30

    Default Re: engine runs rough

    Quote Originally Posted by Slyfox View Post
    thanks Larry, I had one do similar on my io360, ended up cutting out all the baffles inside for both mufflers and made them straight pipe. I also thought of banging on the muffler real quick, but I think I'll pull the muffler and take a look. On the outside it looks great. I do understand the rotax needs back pressure, correct me if I'm wrong.

    I’ve had two do the same thing. The last one I just gutted and called it a day. Plane has been running fine without the baffling in the pipe.

    and the back pressure claims and 4 strokes are kinda funny. The back pressure term when discussing exhaust really only pertains to two-cycle engines in which there was nothing more than a gateway opening exposed by the post on during the engine cycle. This resulted in a need for a tuned exhaust and back pressure needs to ensure the engines would perform at an economical operation range.

    4 strokes don’t really need back pressure in this way due to the inclusion of valves. There are claims that slight back pressure on a 4 stroke engine results in slightly better economy, but these are claims and I have yet to see anyone actually perform the experiment and record their results.

    in looking at the internal “baffle” in these pipes and all of the holes etc etc, I’d argue that the back pressure within that system would change very little with it without that little holey tube inside.

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