AeroInjector tuning questions

[John B]

So from my other thread Getting my S-IIL flying again I installed an AeroInjector on the engine and have been attempting to tune it to get it running as good as possible. The engine is a 2276 cc VW conversion that I built and has about 300 hours total (with a different carb) and only a few hours since a rebuild due to sitting for a long time.

So the engine is a 2276 cc and the fuel system is plumbed from the tank to a fuel filter, to an electric fuel pump, to a fuel pressure regulator set at 1.5 psi (book says 1-2 psi), and then to a shutoff valve and then to the carb. I do not have an EGT installed but I have a narrow band air-fuel ratio gauge installed.

The AeroInjector is a 32mm version and the engine runs ok but should do better. Right now at idle and just off idle the mixture is lean and as throttle is increased, the engine richens up. It idles fine but just off idle there is bit of a lean misfire with slow throttle advancement. At full throttle it is running a bit rich. I still have the needle in that came installed in the carb. I assume it is a #2 needle since I have the #1, the #2.5 and #3 in the package that came with the carb. I have screwed the needle in from the base setting (start of taper at edge of slide) to attempt to get the high speed operation leaner. I'm thinking I have it in far enough that the untapered portion of the needle is in the fuel orifice at low speed resulting in the lean mixture at low speed and rich at higher power settings.

I did fly the airplane for about 30 minutes today and it did OK but like I said should be better.

So, I have some thoughts but wanted to get the opinions of those that have gone before.

1. One thought is to lower the pressure on the regulator to 1 psi to see what that does. My thinking is that lowering the pressure would have a more dramatic effect at high power than at low power and should lean out with higher rpm once the idle is set.

2. Otherwise I'm thinking I need to install the #1 needle, which should lean out the top end when idle is correct.

Is my thinking correct, and which one would you guys that have tuned your AeroInjectors choose? I'd like to especially hear from those with the bigger VW conversion like the 2180 and 2276.

Thanks in advance,

John Brannen

John Brannen

 

[eschrom]

Hi John,

I also have a 2276 with 32-mm Aerocarb (purchased in 2005 IIRC), no. 2 needle installed, and an air/fuel gauge, but no fuel pump. According to the gauge idle is lean but I would never know that without the gauge. It starts easily and idles smoothly. As the throttle goes forward the mixture goes to rich and then somewhat less rich at full throttle. At altitude I lean it back to optimum or slightly rich of optimum. If the air is moving at all and the fuel is sloshing in the tank the gauge fluctuates correspondingly, one of the (minor) negatives about a floatless carb. Another minor negative is that even small power adjustments require a mixture adjustment to keep the gauge happy. The one other complaint I have is that the engine stumbles at the start of a hot takeoff, as I've mentioned in another thread. Not sure yet what the fix for that is. These issues notwithstanding, I'm happy with my AC.

Eleven years ago, before my first flight, I was using an EGT instead of A/F and the engine sounded good but I couldn't get the temperature response the book said I should get during a static runup so I experimented with another needle, can't recall now whether it was the 1 or 3. Whichever it was, the performance was much worse so I reinstalled the 2 and the engine ran like a champ during the flight and since then. What I learned from that experience was that gauges are nice but trust your ear also.

Does any of that help? Other than what the A/F gauge is telling you, in what way should your carb be better?

Ed

 

[John B]

I've played with the mixture on the ground and in flight. I personally do not like how it works and how it can abruptly go from leaning to quitting.. that said I have experimented with it and I know I'm too rich at high power because I can pick up rpm by leaning, and I know it's lean at just off idle because there is a lean misfire. I'm not talking about a stumble from throttle advancement. I can't remember the rpm range but it will sit there at constant rpm missing the whole time. It doesn't quit but will constantly misfire.

 

[eschrom]

Too rich at one end and too lean at the other... maybe a different needle would help.

 

[Mytonic]

A gravity feed system in a Sonerai provides about .5 psi, a no. 2 needle works well at this psi. An increase in fuel pressure will increase fuel flow especially with throttle open, at 1.5psi I would try a needle with less taper or lower the fuel psi.

 

[poormansairforce]

My WaveRunner has mikuni carbs that have no bowls so it just pumps fuel in a loop past the 3 carbs and back to the tank. There's just enough resistance in the length of the return line to keep the carbs fed with fuel. I've always wondered why they don't set the AeroInjector up the same way. A loop past the AeroInjector and back up and over and into the tank would be like a gravity feed.

 

[Flyguyeddy]

Why not call sonex and ask for tech support? Kerry will gladly assist you with it

 

[Flyguyeddy]

Here’s a very good podcast covering this subject

http://sonexflight.com/7/index.html

 

[John B]

Too rich at one end and too lean at the other... maybe a different needle would help.

Well, that is exactly one of the options I proposed in post #1. I was just wondering what others have experienced. The #1 needle appears to be a pretty drastic change, but we'll see.

 

[John B]

A gravity feed system in a Sonerai provides about .5 psi, a no. 2 needle works well at this psi. An increase in fuel pressure will increase fuel flow especially with throttle open, at 1.5psi I would try a needle with less taper or lower the fuel psi.

Again, Those are the 2 things I proposed in post #1. Was hoping to get insight on which one to try first. Had to do some other work so didn't get to try either today.

 

[John B]

My WaveRunner has mikuni carbs that have no bowls so it just pumps fuel in a loop past the 3 carbs and back to the tank. There's just enough resistance in the length of the return line to keep the carbs fed with fuel. I've always wondered why they don't set the AeroInjector up the same way. A loop past the AeroInjector and back up and over and into the tank would be like a gravity feed.

That is an option. We'll se how I do with the other options first but this may be something to consider.

 

[John B]

Why not call sonex and ask for tech support? Kerry will gladly assist you with it

Well frankly because it is a holiday weekend, and Tuesday isn't here yet. Thought I would try here to see if I could get it worked out.

 

[Flyguyeddy]

Well frankly because it is a holiday weekend, and Tuesday isn't here yet. Thought I would try here to see if I could get it worked out.

Listen to that podcast i linked, he goes over it pretty well

 

[103]

I've played with the mixture on the ground and in flight. I personally do not like how it works and how it can abruptly go from leaning to quitting.. that said I have experimented with it and I know I'm too rich at high power because I can pick up rpm by leaning, and I know it's lean at just off idle because there is a lean misfire. I'm not talking about a stumble from throttle advancement. I can't remember the rpm range but it will sit there at constant rpm missing the whole time. It doesn't quit but will constantly misfire.

I think your air filter is restricted experiment with no filter or replace element.

 

[John B]

I think your air filter is restricted experiment with no filter or replace element.

Nope. No filter was installed when I made the first post so it is impossible for it to be a restricted filter. I just installed one yesterday after fabbing the mount and it is now using the same style 4" automotive filter that Sonex sells for the aerocarb.

Yesterday running it with the #1 needle, I think it is improved, but I ran out of time for tuning, so I will have to do that before finalizing judgement, but the next step I'm going to verify fuel pressure using a vertical tube. Should get about 38" rise per psi. I'm not sure when i will have more time to get out there though.

 

[mhflyit]

Make sure you're testing with the cowling on.

 

[John B]

Make sure you're testing with the cowling on.

Yep. That's why tuning takes so long. Cowl off, turn mixture screw, cowl on, test run, repeat, repeat, repeat.