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Thread: Sonex Aeroinjector Tuning

  1. #1

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    Sonex Aeroinjector Tuning

    Can anybody who has installed the new aeroinjector on a Jabiru 2200 Sonex AC give me some advice such as fuel pressure regulator, as compared to reverting to gravity feed,Mixture needle #,carb orientation to get even distribution, etc? Not much luck following their directions for tuning. Thanks. Jim.

  2. #2
    Eric Witherspoon's Avatar
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    At least two Yahoo groups with thousands of posts on this subject. Jabiruengines and Sonextalk. I can't comment to your specific combination, but I've been using the Aeroinjector on the 3300 with the #3 needle, and it was not difficult to get set up. Oh, and no fuel pump - gravity feed only.
    Murphy's 13th: Every solution breeds new problems...

    http://www.spoonworld.com

  3. #3
    Neil's Avatar
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    I can't tell you anything about the Aero Carb, but I suspect it responds in much the same way as the POSA slide valve injector as far as tuning is concerned. I have several hundred hours flying with the POSA on a Sonerai and made precision needles for them at one time. I have mailed needle sets all over the globe with good success but I have since retired and no longer have access to the machinery and tooling to make them.
    Without a pressure regulator the mixture will richen with increased "G" forces. To run steadily under all "G" loads the unit needs to be tuned at a regulated pressure. When setting up the POSA, I started with the idle. Do what ever it takes to get the engine to idle properly with no effort wasted on higher power settings. It is difficult and dangerous to do any tuning if the engine won't idle. I designed an idle mixture circuit for the POSA that helped with this. Don't know if the Aero Carb has an idle circuit. Once a good idle is established (with the airplane tied to a car, tree, fence post or some other fixed object) open the throttle and determine if the engine goes too rich or too lean. If it is too lean, more taper in the needle is needed. Too rich and less taper is needed. Messing with it otherwise is a wast of effort.
    I made needles for the POSA with a difference of .001"taper per inch. There was no rule of thumb as to what taper a particular engine needed because side draft installations responded differently from up draft installations. Up draft seemed to run best. Once a range of tapers was established with the POSA, fine tuning got down to changes of .0005" per inch in the taper of the needle. In some cases it was necessary to have a couple different tapers blended together for an ideal mixture curve but generally the correct straight taper would give the proper mixture in the mid ranges and be slightly rich at full throttle for climb. A difference of .001" of taper equated to about 150deg F on the EGT.

  4. #4
    Eric Witherspoon's Avatar
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    I don't think Jimbo's going to have to custom-make or even necessarily modify any needles.

    No, the Aeroinjector does not have an idle circuit.

    Most of the 2200 operators are using the #2 needle. At idle, clearance between the needle and the housing is a significant contributor to the flow rate, so they tend to be a bit rich at idle. Some have found it to be so rich at idle that they use the mixture control. So set it up to be too rich at idle. On mine, say an average day (mid 60's F), it will idle at 780-800 rpm. Then, if I lean it, it will pick up to 1000-1100 rpm - that's how rich it is. Then, at the higher throttle settings, the opening defined by the needle taper takes over. The most common mod is just the slightest "shave" at the full-open end of the needle - I believe to give a bit more richness right at takeoff power settings. There has been one person that I know of who built up the needle with solder right at the "idle" end of it and then very precisely machined just the slightest bit larger diameter there - to tighten up the clearance between the needle and the housing to reduce the "rich at idle" tendency. But from what I can tell, nobody (at least who will talk about it) has followed this lead.

    To the original question - I would recommend trying it with gravity feed only.
    Last edited by Eric Witherspoon; 01-29-2012 at 08:16 AM. Reason: Idle rpm - adjusted based on what I saw yesterday.
    Murphy's 13th: Every solution breeds new problems...

    http://www.spoonworld.com

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