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Thread: Carb sync? Never again.

  1. #51
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    Default Re: Carb sync? Never again.

    G'morning Rodney
    I believe the title to this thread is a bit misleading. I strongly believe we should all sync the carbs on a regular basis BUT unless you are able to keep "the green light in the middle" through all RPMs from idle to full throttle (It was always a compromise for me) then maybe a modification to the balance tube might be helpful.
    Going to a breakfast flyin this morning. We'll see how another 2 hours air time goes.
    Take care
    Don

  2. #52
    Senior Member Rodney's Avatar
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    Default Re: Carb sync? Never again.

    Kitfox 2009

    Ya I guess we kind of did the "thread creep" thing.

    Sure hope you have a great flight n breakfast.

    Still, a lot of valuable info in this thread n a lot of fun looking at the
    different ways to build a balance tube. Like yours the best. Simple n very cost effective to build. And it works.

    Maybe some day Canada n the FAA will get it worked out so those of us on a drivers license medical can visit you guys in Canada 🇨🇦. Sure would be nice

  3. #53
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    Default Re: Carb sync? Never again.

    Yeah, good luck with that Rodney!!! I wrote to the RAA and AOPA about this and the answer I was given at the time wasn't very promising. I'm not sure if there are many of us on the sport pilot that care to venture into Canada. I was flying on floats for a few years and wanted to make it up there.

  4. #54
    Senior Member jiott's Avatar
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    Default Re: Carb sync? Never again.

    Regarding the bigger balance tube: There is such a thing as tuning the inlet manifold system volume for max performance at high power levels. Do you suppose that the Rotax engineers may have done this? Has anyone with these larger balance tubes done any kind of testing to make sure you have not degraded your high power performance? Just asking.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  5. #55
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    Default Re: Carb sync? Never again.

    HI Jim
    I never have been able to have the carb mate green light in the middle through all RPMS from idle to 4000.
    So this is what I did..
    I installed the over size tube and adjusted both idle stop screws to give the smoothest possible idle at about 1600..I think the 80 horse engines are smoother at these low rpm.
    Then I shut down and hooked up the carb mate.
    Restarted and immediately ran up to 3000,4000. Adjusted the linkages to center the green dot at the most sentsive setting. It is steady at all RPMS above 3000.
    Shutdown and reinstall oversize tube and go flying.
    Made a breakfast trip this morning and came home direct over the top at 8500. Ran great. Pretty hard to tell is it was any better than normal. At that elevation I usually adjust a prop and throttle for about 5000 rpm and 27 inches. About 75%power according to rotax charts.The ias is only about 95 mph. We were flight training with very cute CASARA spotter so was not in a hurry!

  6. #56
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    Red face Re: Carb sync? Never again.

    Sorry Jim
    That probably didn't answer your question. Not sure if you would call that "testing".So take this idea and results as a very seat of your pants summary. It may not help at all.
    The flight training was a lot of fun though,especially for an ole guy.
    Cheers
    Don

  7. #57
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    Default Re: Carb sync? Never again.

    The Hal Stockman cross over tube conversion is done and it works as others have said. I added 1/8 NPT hole to install a nipple for CarbMate pneumatic sync. I also used a one inch coolant hose across the manifolds. I did the mechanical sync as carefully as I could and when the CarbMate was hooked up, the carbs were in the green at 3500 rpm and at idle with no further adjustment needed. The rough spot between 2500 and 3500 rpm is gone.
    Attached Images Attached Images

  8. #58
    Senior Member Wheels's Avatar
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    Default Re: Carb sync? Never again.

    I'm pretty impressed with what you guys are seeing. I imagine a cracked tube or broken seal would act like a carb boot failure. Am I right? Just wondering what the failure chain looks like before we go there. I don't see any extra links in it from the old aluminum and rubber hose assembly that came with the engine.

  9. #59

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    Default Re: Carb sync? Never again.

    Fellow Flyers,
    I finally did the enlarged balance tube mod on my 912UL over the last couple weeks and have flown for about 2 hours now and can firmly confirm that:
    -It runs very smooth over the full throttle range
    -No change in my performance numbers except that it feels lot smoother overall. (it feels more powerful)
    -Cold start is like a car with no shudder or vibration.

    Not enough time to say if it changed my fuel consumption but I would assume it will run more efficient just because of all that smoothness and both banks running hand in hand.

    I will remember to take some pictures next time but all I did is that I drilled and taped the existing balance tube holes to 3/8"NPT and screwed in the 3/8" 45 degree male to female fittings in them. I drilled out the fittings ID to remove any casting imperfections and increase the ID a bit.Then I took a 3" long 3/8" NPT nipple and cut it in 2 halves. Screwed each half into the fittings added. Connected both sides with a 9/16" Vacuum hose from PartSource. All fittings were thread locked on final assembly.
    Feel free to contact me with any questions and I will consider doing all the machining and supply parts as kit for anyone who would like to give it a try for something around $300.

    Happy Skies,
    Harry

  10. #60
    Administrator DesertFox4's Avatar
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    Default Re: Carb sync? Never again.

    Thanks Harry. I have recently talked to a couple Rotax powered Kitfox owners looking into this modification.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


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