SonexBuilders.net

Hi all,
After trying first with #2 needle and later with #2.5 and then changing back to #2 I got disparate to solve the idle problem. With #2 needle it was very rich at idling and ok on high power. I then tried #2.5, idle very well but was very rich on high power. Leaning it would stop the Aerovee idling. After changing to #2 the idling problem came back very badly and trying to lean make the Engine run hot and still did not idle properly. I have to pull the mixer control out almost until fuel cut off to keep the Engine running.
Due to desperation I decided to measure the 1, 2, 2.5 and #3 needles taper hight at 5mm intervals, length of taper from the tip and the needles diameter.
I came to an interesting conclusion. The taper of needle #2 and 2.5 are the same until about 2/3 from the tip. I was puzzled why the engine did not idle properly with needle #2 and did idle well with #2.5.
After measuring the needles diameter with a micrometer I found the problem. The diameter of the #2 needle is 0.05 mm smaller than #2.5.
Needle #2 is 3.14mm while needle #2.5 is 3.19mm. That means on idle, fuel is leaking passed the needle and make it rich without be able to lean.
After borrowing a #2, 3.19mm needle from a Onex builder what I put in today, the results are amazing. After some needle adjustment the engine idle and run on high power without hesitating and without any mixer control adjustment needed. It is performing like a different Engine. It can now during cruise be properly leaned with the mixer control. It have flown today 1 hour with 3 touch and goes not needing any adjustment to the mixer control.
After 10hrs of test flying now proper test flying can be done.
Peter Sonex #1430, Aerovee 2.1

You have discovered the problem with the needles except you are looking at the diameter instead of the taper length and angle. Here is a copy of my post last month.
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 holde. 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.

OneX 107

I have measure the 1, 2, 2.5 and #3 needles taper high at 5mm intervals, length of taper from the tip and the needles diameter.