Aerocarb revision?

[gammaxy]

An Aerovee with the Aeroinjector idling rough is not normal.

I agree, in my experience with my Aeroinjector, a rough idle is not normal. I can imagine that it might be possible to end up too rich at idle once the WOT setting is dialed in, but I would expect it to at least run smoothly with the mixture leaned.

After I got a new #2 needle with the correct diameter from Sonex (after first trying with a borrowed one) and a few adjustment
it is a different engine.

I've followed your posts about this with great interest. I admit, though, that I'm still skeptical, but not so skeptical that I wouldn't give it a try if I was having issues. I imagine Sonex isn't convinced since they don't appear to have publicly addressed this? I did measure my needles after reading your other posts and did find them to be of the two diameters you mentioned. Unfortunately, I haven't measured my #2 needle since it is installed in the airplane and I'm reluctant to mess with something that seems to be running well :-) I admit that I just don't know enough about how fuel flows past the needle to really form an opinion on whether such a small diameter difference matters. But, it sounds like after going around with various needles we both found the #2 needle to work best.

[mike.smith]

An Aerovee with the Aeroinjector idling rough is not normal. Most likely the needle is faulty.

I think everyone's experience varies. I have had 150 trouble free hours and all my temps are in the green, even when idling on the ground on a hot day. So I'm very happy with my needle and my idle. For me, no sense changing something if it works reliably through the full range of throttle movements.

[Onex107]

I've posted on this several times, but it needs repeating. Tighten the ball socket in the needle holder and measure the dia. of your needles. A needle that is .001 under the .125 diameter is difficult to adjust at idle because the fuel is leaking around the diameter, not just on the flat side. Some of the older Aeroinjectors came with brass needles. I had new needles made from drill rod that is exactly .125. The flow at idle is small enough to be effected by this. I think the dealer needles are made from "wire" that has a larger manufacturing tolerance than drill rod (it's less expensive), and my needles varied from .001 over to .001 under. In my case, I went on to the #3 needle design, which gives me an excellent WOT and IDLE at the same mixture setting. I only adjust the mixture at cruise to raise the EGT a little and don't touch it again until the next flight. 103 hours and counting.

[kevinh]

I've posted on this several times, but it needs repeating. Tighten the ball socket in the needle holder and measure the dia. of your needles. A needle that is .001 under the .125 diameter is difficult to adjust at idle because the fuel is leaking around the diameter, not just on the flat side. Some of the older Aeroinjectors came with brass needles. I had new needles made from drill rod that is exactly .125. The flow at idle is small enough to be effected by this. I think the dealer needles are made from "wire" that has a larger manufacturing tolerance than drill rod (it's less expensive), and my needles varied from .001 over to .001 under. In my case, I went on to the #3 needle design, which gives me an excellent WOT and IDLE at the same mixture setting. I only adjust the mixture at cruise to raise the EGT a little and don't touch it again until the next flight. 103 hours and counting.

That is super useful - thanks.

re: loose tolerances on the needle diameter

If this is true - I wonder if this is an example of "pennywise pound foolish" on Aeroconversions' part? Aerocarbs have a 'rep' of being finicky, but I bet 70% (or whatever) of the problem is people not carefully following directions and 30% is the problems you described. It seems like in the scheme of things fixing the problem you describe at manufacture time would really help the aerovee/aerocarb reputation in homebuilt world (for very low cost to sonex).

[bakfly]

Believe me 0.05mm (0.0025") thinner needle make a lot of different during idling. We had the same problem with the another Aerovee Sonex build in Adelaide South Australia. After 4 or 5 hours test flying and constantly adjusting the #2 needle trying to get it idling properly, they desided to get another #2 needle from Sonex. When they installed the new needle in the holder they noticed that the new needle fitting nice and tight in the needle holder while the old one fitted sloppy. They are now able to adjust the needle properly for idling, WOT and Cruise. They completed test flying without any more needle problems. After this problem is solved you never have to use the mixer control for idling. I only use it to get beter economy during cruise.
Peter
Sonex 8464

[wlarson861]

One thing I have noticed is we all want it to run perfect at first run. It AINT gonna happen. Tune the carb to give you the proper EGT temp difference and go fly. As the engine gets broken in things like idle and peak rpm and leaning will improve. If I knew then what I know now I would have flown about 15 to 25 hours before I ever revisited the tuning process. The engine needs to break in before you can determine that something needs to be adjusted.