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Thread: Precision tuning the Rotax 912 UL/ULS

  1. #11

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Quote Originally Posted by Delta Whisky View Post
    Many thanks for the video - I'm interested in any details you can share (remember?) regarding the O2 sensor and the threaded bung or receptacle you used. As far as displaying the AF ratio - is there any chance a volt meter with a nearby conversion table could work? I'm also assuming that by using one O2 sensor in the middle of the muffler you made corresponding carb set ups and didn't worry about any minor differences between the left and right sides.

    Your timing couldn't be better for me. Maybe you saw in a different thread my exhaust stinger departed the aircraft during its last flight. There is some evidence it might have been related to insufficient clearance between the cowl and the exhaust stinger but there is also considerable evidence it was the result of a vibration issue. Without the capability of a thorough vibration test I'm committed to address both possibilities - and it won't hurt to make the engine as smooth as possible for comfort reasons. Anyhow, when the new muffler shows up, I'll be ready to add the O2 sensor if a reasonable ($$) way to interpret the output is available.
    Glad it helped! As far as the bung, you are correct in the assumption that it was centrally located to gain an "average" understanding of what was happening between the two sides and all adjustments were mirrored from one side to the other. In a perfect world. we would pull the muffler, connect a single downpipe to each side and have an AFR meter for each bank of cylinders. If I had the free time and extra funds I would make that happen, but I own an airplane... so broke as a joke haha.

    As far as interpreting the output, there should be a way with a multimeter. Youll receive a signal ranging between 0 and 5V. You could linearly extrapolate the points between these voltages and correlate them to a AFR rather easily. I believe 0V is roughly 7.4 and 5V would equate to about 22.4 - I can verify these numbers for you if youd like.

    In the coming weeks when I finally align and complete a few more projects ill be taking a stab at that arduino code for an AFR meter. That would be a rather small investment for everyone to make and would be a much faster means to collect data than comparing a dynamic value to a data table.

    Please post up any of your progress on this and any questions. Id love to actively participate in your tuning while posting in this thread so people are able to see and read through your process in real time - I got too frustrated chasing the rabbit hole trying to figure this all out the first time to make a video that wasnt comprised of mainly curse words.

    109JB, thank you for your input on this as well. Glad to see that others are noticing the same thing I am and that our data supports each others findings - overly rich in idle was a major root cause to the excessive vibrations I had at low RPM. Correcting that idle circuit had a HUGE impact on the rest of the engine tuning and starting there is 100% what I recommend to anyone that is going to be moving forward with this.

    Now, looking at this thread title, I do not think its clear the information that is being shared in this thread - anyone have any suggestions as to a better thread title to get this information out to as many 912 folks as we can?

  2. #12
    Administrator DesertFox4's Avatar
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    Default Re: Precision tuning the Rotax 912 UL/ULS

    For more clarity on the content of this thread, I can go back and change the title on all posts but have to do them one by one so let me know soon what you think is a more concise title before too many more posts.
    I did add some generic “tags” below for easier searches in the future. Anyone can add more “tags”at anytime that will help members in the future find this in-depth thread on precision tuning a Rotax carb equipped engine.


    DesertFox4
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  3. #13

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Quote Originally Posted by DesertFox4 View Post
    For more clarity on the content of this thread, I can go back and change the title on all posts but have to do them one by one so let me know soon what you think is a more concise title before too many more posts.
    I did add some generic “tags” below for easier searches in the future. Anyone can add more “tags”at anytime that will help members in the future find this in-depth thread on precision tuning a Rotax carb equipped engine.
    thank you sir! If we get some input as to better titles then I’m all for a change as long as it doesn’t inundate you with more crap to do (as if you’re not busy enough).

    Nick

  4. #14
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    Default Re: Precision tuning the Rotax 912 UL/ULS

    How about "Precision Tuning the Rotax 912ULS"?

    Rick

  5. #15

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Precision tuning the Rotax 912 UL/ULS - now that I like.

    also currently building a set of intakes to bring these carbs closer to centerline while still allowing us to use the KF engine mount - nice thing as these intakes will already include the 1” crossover port.

    mild stew for prototypes, fingers crossed this works and I’ll be producing a set out of 304SS for Bane.
    Attached Images Attached Images

  6. #16

    Default Re: Precision tuning the Rotax 912 UL/ULS

    Well yesterday was a success - the plane spent a few hours in the sky and I was able to monitor AFR throughout the flight.

    During cruise flight at 5400 rpm I’m getting 12.8:1 on the head. This is beyond exciting. Now there is still a bit of tuning to be done at the 4800 rpm range as the plane reads an AFR of 14.1:1 - I’ll be ordering a few new needle jets to see what I can make happen there. Lastly idle is a bit on the rush side reading about 11.8 at 2200 rpm but it’s dead in 12.8 at 1750 rpm. I’ll be playing with the idle jets a bit as well to see what I can do with this due to the fact I’ve got the idle mixture screws set at only 1/4 turn out from fully seated.

    overall the plane performed flawlessly and had zero issues with the maiden voyage. Heck yes back in the sky!

    79D28613-2E16-441C-A9EC-F3FF7FCBD90F.jpeg

  7. #17
    Senior Member Slyfox's Avatar
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    Default Re: Precision tuning the Rotax 912 UL/ULS

    let me ask you this, have you done anything with the floats. Seems the actual floats are junk
    steve
    slyfox
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  8. #18

    Default Re: Precision tuning the Rotax 912 UL/ULS

    I have. I ordered the blue floats that are supposedly better than the stock floats as they are often mentioned to not deteriorate and absorb fuel over time. I did also end up having to set the fuel height in the bowl numerous times and current measurements have the float armature measuring 13.5mm from the carb edge as opposed to the 10.5mm constantly mentioned.

  9. #19
    Senior Member Slyfox's Avatar
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    Default Re: Precision tuning the Rotax 912 UL/ULS

    I've been having a lot of trouble with my carbs, flooding out while sitting without the engine running, running rough at cruise. I ordered the blue ones also, will be here Monday.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  10. #20

    Default Re: Precision tuning the Rotax 912 UL/ULS

    What do you have the float armature set to? Try 13.5 mm and make sure to do a full throttle grind run up before taking off. Run up for well past a climb out duration to make sure the carbs are refilling quickly enough after the adjustments

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