by Onex107 » Tue Apr 30, 2024 9:46 am
I did some experimenting with needles, making seven in total. I made the needles from .125 drill rod, grinding the tapers on a surface grinder using a Sine plate. I found the three needles supplied were slightly under size on the diameter. The needle has two, what I call, sweet spots. One for idle and one for wide open. The needles, 1 through 3, have different angles of taper. As the angle increases, the two sweet spots get closer together. I found the wide-open sweet spot to be at about .082 needle thickness. And the idle sweet spot is nearly at cutoff. The ideal needle has both these spots located within the slide movement from idle to wide open. In the beginning I tuned for wide open like Sonex suggested. With the #2 and #2 1/2 needles I still had to lean the mixture to get a decent idle. As it turned out, my #7 had almost the same measurements as the Aero Injector #3. So, I tried the #3 and my problems were solved. My wide-open setting was made with the mixture about halfway out, so I had the chance to go leaner or richer. Take off was smooth at 3000 rpm and idle at 900 had no problems. I didn't have to lean when I pulled off the runway. I didn't change the mixture until I was at cruise and then only to lean for a good EGT. From one flight to the next I didn't touch the mixture.
When adjusting the needle. Mark the beginning of the taper, on the bottom of the needle, with a file. The shiny mark is more accurate and easy to see. Line it up at the edge of the opening and count the number of turns to your setting. Adjust the needle 1/4 turn at a time. That gives you a repeatable point to begin adjusting for a good wide-open setting. Just sayin.
OneX 107
N2107X