I have a Sonex B that is 99% complete and is so close to flying. I installed a new Jabiru 3300 and an Aeroinjector carb. But I just can’t get it to run well enough to fly. At full rich mixture I cannot get full power, the motor bogs and runs rough. Max RPM attained is about 2300. If I lean the mixture quite a bit it’ll run smoother, but if I lean it any more, the motor stops. At this mixture setting my EGTs are well over limit, and I still can’t get full power.
I’ve tried so many things to fix this. I’ve tried the 1, 2 and 3 needles. I’ve made so many 1/8 turn adjustments to the needle carrier. I’ve done a cylinder leak down check. I’ve disassembled and reassembled the carburetor. I’ve re-read the Aeroinjector owner’s manual many times. I’ve sought the advice of Nathan and Cris at Sonex, and Nick at Jabiru. They’ve all tried to help, but nothing I’ve tried has made any noticeable difference. Has anyone else had any similar issues? I’m really frustrated. This plane should have been flying months ago.
Welcome to the forum. Sorry to hear you are having trouble. I’ve got some AeroInjector experience and will try to help. Which needle are you currently running? I think my AeroVee came with a 2, 2.5, and 3 needle. It’s happy with the 2, and the 2.5 was too rich. The #1 seems like way too skinny for a 3300, since it should burn about 1.5 times the fuel of the AeroVee at WOT. Hopefully some of the 3300 guys will chime in with what they used.
If it is bogging at WOT and full rich, with some improvement by pulling the mixture, the needle needs to go in (leaner) for sure. From memory I’d say from full rich to peak RPM should be a difference of about 50-100 RPM. Bogging at 2300 says the thing is drowning in fuel.
There are two things that make needle adjustments more repeatable:
Deform the threads on the carrier a little, so there is friction when you turn it. I squashed mine just a little in my bench vise.
Get a ball bearing that just about fits in the hex of the carrier. That way when you tighten the locking plug (set screw in the manual), it only hits the ball and does not torque the carrier out of position.
If I didn’t have anything to go on, I’d start with a #2.5 needle and see if I can get it to run nicely at WOT. But for sure I’d defer on the needle selection to the 3300 guys.
I had similar issues with my Jab 3300 and AeroInjector. Having said that, I believe I am now setup correctly and the engine runs great. All of the 3300 guys are either using a 2.5 or 3 needle. I settled on the 3 - and then turned it 1 1/4 turns lean into the AeroInjector. I found the trick was to adjust the idle first - and then see where you ended up at WOT. When I used the 2.5 needle, I could get the idle mixture about correct - but then was too lean at WOT. So I moved to the #3 needle, turned it in the 1 1/4 turns for a good idle - and the WOT felt about right. I can now hit 3300 RPM at WOT.
Feel free to reach out to me if you would like to talk.
On my 3300 I set the idle mixture and rpm first. (#3 needle) Then I set the slide travel, by limiting the throttle lever travel, to keep the EGTs from going too high at WOT. The slide is NOT opening all of the way.
With the temperature in the mid 30s Fahrenheit I’m staticing around 2700 with the 64” pitch Sensenich composit prop. In the summer I getting over 2800. I’m very happy with the performance.
Your prop will impact your RPM a lot. N815EC stated that he is using a 64” Sensenich. I’m using a Prince P-Tip 54/62 which is considered a “Cruise” prop - and typically yields a bit lower RPM. Having said that, I got 3100 static RPM and can easily get 3300 RPM in the air. What prop are you using?
I have had two experiences on ferry flights with that engine with high power restrictions, especially on early morning humid day runs. In both cases it was related to inadequate air intake through the standard Sonex air filter. It was confirmed by doing test run with the filter removed. If that cures the issue, use a K&N air filter.
I had very simular concerns about the small filter, and initially went with the K&N filter, about twice the size/area, and have not had any problems about not getting WOT rpm on my aerovee. Tom makes a very good point!
I’ve got a K&N RD-0720 filter. 2.5” diameter, 6” long. Connects to the AeroInjector with a 2.25” silicone elbow. The monster AeroVee gets plenty of air.
