AeroInjector Problem Solved

[Onex107]

I, like many of you, have been frustrated with adjusting the AeroInjector for a full range of throttle. This is my story and I’m sticking to it.
I started with the #2 needle like suggested. It worked reasonably well for the first 25 hours and then, for some unexplained reason, went lean and couldn’t be adjusted. Sonex recommended going to the #2 ½ which worked at the top end, wot, but had to be leaned almost to cutoff for a smooth idle. If I didn’t adjust the mixture during taxi it would die from being too rich.
Some of you are making mixture adjustments with every throttle change. That was unacceptable for me. I started by measuring everything and found nearly a half turn of play in the ball joint of the needle holder. Rather than shim or squeeze the holder to tighten it up, two of us designed and had made a new holder that uses a disk instead of a ball end on the set screw. The results are when you make a one eighth or one quarter turn adjustment you get exactly that In linear motion.
The next problem was the needle. Obviously the air intake from idle to wot is not parallel with the #2 or #2 ½ needle volumes. They have to be adjusted for wot and that leaves the idle setting too rich. I read of one owner that filed one of his needles to make it match the air intake volume.
A friend and owner in Florida suggested I try the #3 needle that he had success with. I did and hit the jackpot. In theory, the #3 has enough slope, in the same length needle, to allow the mixture to be correct at idle and still have enough fuel flow at wot. It works.
I installed the #3 as per the book. I adjusted in one half turn increments to make it leaner. After 2 ½ turns leaner, at full rich, it started with a smooth idle (1000 rpm). Static rpm at wot was 2930 with about one inch of mixture. The idle was smoother at this setting also. I have flown the setup for 2 ½ hours without touching the mixture. Max rpm at cruise is 3200 and all temperatures are good. At 35 degrees outside temp., the egt’s are 12 to 1300 and the cht’s are all below 350. I’ll continue to report this as I build hours on the setup. My engine is at 39 hours ( hobbs) and not completely broken in.

[MichaelFarley56]

I'm really glad to hear you discovered the size needle that works for you! I'm one of those people that needs to make mixture adjustments prior to every big throttle change, so I may try to go to a #2.5 or #3 needle just to see what it's like. I'm fine with mixture adjustments but it would be nice to have things a little more "stable" in that regard.

Thank you for the report and I hope the rest of the Phase 1 has been going well for you!