AeroInjector Tuning

[gethomas]

Having trouble getting my recently assembled AeroVee2.1/AeroInjector tuned and running as specified in the manual. At full throttle and full rich mixture, static rpm is 3100. The problem is the EGT quickly going to over 1450 and with leaning it DROPS to about 1320 just before engine runs rough. I believe this indicates a too lean mixture. Have tried mixture needles 2, 2.5 and 3 with same results. Tried reinstalling/sealing intake manifold thinking air was getting in somewhere. Any ideas of what's wrong?

[Rynoth]

It does sound like it's too lean, but you didn't mention adjustments to the needle position. What happens if you back the needle out a full turn? Remember that to enrichen the mixture at the needle you'd turn the hex screw counterclockwise.

Also are you making sure that when inserting the locking screw that the needle-carrier screw isn't also being turned? Visually check for any motion of the needle while inserting the set screw, and consider peening the needle screw threads slightly to make it more resistant to turning. If the locking screw is turning the needle screw during tightening it will be putting the needle into a leaner position.

Here is some more discussion on the topic of the needle and set screw:
viewtopic.php?f=21&t=5338&p=40447&hilit=needle+screw#p40447
viewtopic.php?f=7&t=4447&hilit=needle+screw

[mike.smith]

A few questions: Where are the EGT probes located? Have you noted the CHTs? How long are you running the engine? Have you been able to note any colors of the exhaust?

[gammaxy]

3100 rpm static sounds about right to me, so you're probably at least in the ballpark. Are you using the Sensenich 54x44?

As an additional sanity-check, did you notice whether the RPMs increased or decreased as you leaned the mixture? It's been a long time since I did the EGT test for tuning, but I do always get a fairly noticeable RPM increase when leaning from full rich on the ground at WOT.

The #2 needle tuned pretty close to the default position works pretty good for me. That you don't seem to be able to change mixture even with a needle change is surprising to me. In my experience, a single turn of the needle can change things drastically.

Have you performed a fuel flow test to verify your fuel system is not limiting you? I measured ~12GPH for the last 2 gallons in the tank. I've since removed the fuel flow sender from the line and suspect it flows much more now.

[gethomas]

It does sound like it's too lean, but you didn't mention adjustments to the needle position. What happens if you back the needle out a full turn? Remember that to enrichen the mixture at the needle you'd turn the hex screw counterclockwise.

Also are you making sure that when inserting the locking screw that the needle-carrier screw isn't also being turned? Visually check for any motion of the needle while inserting the set screw, and consider peening the needle screw threads slightly to make it more resistant to turning. If the locking screw is turning the needle screw during tightening it will be putting the needle into a leaner position.

Here is some more discussion on the topic of the needle and set screw:
http://sonexbuilders.net/viewtopic.php? ... rew#p40447
http://sonexbuilders.net/viewtopic.php? ... edle+screw

Turning needle CCW (mixture richer) the engine starts u=running rough. EGT high is lower but drop with leaning is still there. I incorporated a setcrew piviot used by another builder uses; set screw does not move.

[gethomas]

A few questions: Where are the EGT probes located? Have you noted the CHTs? How long are you running the engine? Have you been able to note any colors of the exhaust?

Probes located in exhaust manifold a few inches from exhaust port as specified by Sonex. Running about 2-3 minutes at full throttle the will CHT go to 400deg. Some black smoke with #3 needle.

[gethomas]

3100 rpm static sounds about right to me, so you're probably at least in the ballpark. Are you using the Sensenich 54x44?

As an additional sanity-check, did you notice whether the RPMs increased or decreased as you leaned the mixture? It's been a long time since I did the EGT test for tuning, but I do always get a fairly noticeable RPM increase when leaning from full rich on the ground at WOT.

The #2 needle tuned pretty close to the default position works pretty good for me. That you don't seem to be able to change mixture even with a needle change is surprising to me. In my experience, a single turn of the needle can change things drastically.

Have you performed a fuel flow test to verify your fuel system is not limiting you? I measured ~12GPH for the last 2 gallons in the tank. I've since removed the fuel flow sender from the line and suspect it flows much more now.

Prop is Sensenich purchased from Sonex. RPM drops with leaning. Fuel flow test with 4gal in tank; timed 4min30sec to drain a the injector connection point.

[sonex1374]

Running about 2-3 minutes at full throttle the will CHT go to 400deg. Some black smoke with #3 needle.

gethomas,

Running the AeroVee on the ground fro 2-3 minutes at full throttle will definitely heat up the engine to red-line, and no amount of carb tuning will prevent that. The engine simply doesn't have the cooling capacity on the ground without some additional cooling equipment. This isn't a good test of what's happening with your engine.

Although there is no universal guide to needle selection, the most common needles for an AeroVee are the 2 and 2.5. The 2 can be adjusted to provide sufficient fuel flow at full throttle, but will likely be rich at low throttle. The 2.5 will make low throttle a little leaner when adjusted to the same full throttle fuel flow. Either can work. The #3 needle might not be a great choice for an AeroVee because it's really designed for more fuel flow. You can try it, but I wouldn't start with that needle.

It sounds to me like you are making too large of adjustments during your tuning process, and inadvertently overshooting the optimal position on each needle you've tried. I would recommend putting the 2 or 2.5 needle in, setting it to the default position as per the manual (which is usually slightly rich at full throttle). When you're ready to make a needle adjustment, make them small (1/4 turn initially, then 1/8 turn or less as you zero in on the sweet-spot).

Using EGT values for initial tuning is going to be frustrating - you don't know what normal is or where peak is for your particular engine, so I'd focus on other parameters first. You can observe the rpm and EGT trend (especially when leaning with the mixture knob), and that will tell you if the current needle setting is rich or lean. Pull the mixture knob out a bit and rpm increases and EGT increases, you're rich. If rpm doesn't increase or sightly drops, and EGT starts to decrease, you're lean. Before you make an adjustment to the needle you need to know exactly how the engine is behaving, then determine whether you need to enrichen or lean the needle. After that, it's simply a matter of making a small adjustment and trying again. Overdo the adjustment and you'll end up just chasing it round and round.

Lastly, you'll want to be comfortably rich enough at full throttle for first flight. The AeroVee will run and make nearly full power on reduced fuel flow, but it's really hard on the valves and head. You'll want a little extra fuel flow to keep things in order. This is one area where a fuel flow gauge really helps out, but it can be done without one as well. If you're needle is adjusted a touch rich at full throttle, you can always lean a bit using the mixture knob, but there's no way to make it richer. This is why you'll want a comfortable margin on your needle position.

Jeff

[gethomas]

Jeff Shultz:
"You can observe the rpm and EGT trend (especially when leaning with the mixture knob), and that will tell you if the current needle setting is rich or lean. Pull the mixture knob out a bit and rpm increases and EGT increases, you're rich. If rpm doesn't increase or sightly drops, and EGT starts to decrease, you're lean"

Regardless of the needle# or screw position, I can not get the first trend you describe (rpm/EGT increase) trend you describe. Always get rpm drop and EGT decrease as mixture knob is pulled toward lean. With needle screwed CCW to engine running rough and black smoke I get the same rpm drop/EGT drop trend.

[Onex107]

I'll jump in here with my nickel. First of all check the needle holder for play in the ball socket. You should be adjusting in no more than quarter turns of the screw and my needle holder had nearly a half turn of play. Tighten it up best you can until the play is nearly gone. Second, mark the bottom of the needle with a file. A shiny mark is much more accurate than a felt tip marker and more repeatable when removing and replacing the needle holder. Start with the file mark at the edge of the opening. I call this the "o" point. All settings start from here. Count the number of turns from this point to the final setting so you can repeat it. The angle of taper on the needles increases with each number and as the angle increases the sweet spot for WOT and the sweet spot for IDLE get closer together so as you set it up for WOT the IDLE mixture will get leaner with increasing needle number..
You are probably testing without the cowling installed. I find that my engine doesn't run very smoothly until the intake manifold warms up. This requires about five minutes of running at 12-1500 rpm, with the cowling buttoned up until the oil temp hits 100 degrees plus and cylinder heads are at 200 . I know ---- you can't adjust the Aeroinjector with the cowling on, just don't expect perfection until you fly it buttoned up.
My setting, for what it's worth, is with a #3 needle, adjusted clock wise from the "0" point 2 1/4 to 2 3/4 turns. This will probably vary from one AeroInjector to the next due to manufacturing tolerances. For instance, my needles varied in diameter a few thous. I run with the mixture pulled out about half way. From there I can go a little richer to cool a hot cylinder on climb out and a little leaner after reaching cruise to raise the EGT's for economy. And---after flying with the engine fully warmed up it idles at 900-1000 without a mixture change. I don't change my mixture until the next climb out. This must be very confusing for a new builder. Your engine is new, and tight, and is going to run a little hotter than normal until it breaks in. Adjust until you get a good WOT as per the instructions. The temps you will see with a fully warmed up engine during flight will guide future tweaks as the engine breaks in. Many builders have given up on the Aeroinjector in frustration because they don't understand it. Stick with it. It's a simple, less expensive, installation, and it works as advertised. 300 hours with no change. I knew 2 cents worth wouldn't be enough.