SonexBuilders.net

Hey Bryan,

A few quick questions:

First, what did you set as your compression ratio? Are you at 8.0 to 1? Also, what prop are you using? The standard Sonex recommended 54x44, in either Sensenich or Prince? What is your field elevation? Which air filter are you using? Is the engine running smoothly?

To me, 2750 RPM at full throttle is a little low. If it's over 2900 I wouldn't be worried but this could be any of a few possible issues. First, your throttle cable may not be allowing full aeroinjector throttle plate movement. I would consider removing the air filter to check for throttle travel, and while it's off, do a quick test run without the filter. If that's an issue (dirty filter) that could be causing some of your problems. If that's not the case, I'd next focus on the injector needle.

I'm using a "stock" (unmodified) #2 needle in my AeroInjector as well. I'm sure you've read the manual and know where to start adjustments, but just for the fun of it I'd run through the tuning procedures again. What sort of RPM rise/loss are you seeing when you're at full throttle and full rich mixture and slowly lean out the mixture? As a guess I'd also venture out and say you're maybe a little lean for the conditions. I try to keep my needle adjusted so I don't see much over 1200-1250 max EGT during a full throttle, full rich mixture climb. That's what the factory recommended for me. I'm sure you've read it, but making small needle adjustments of 1/8 of a turn can make a big difference.

Don't be surprised if you need to lean out the mixture at low power operations like taxi and idle. That's pretty common. I for one will have my mixture leaned almost halfway of the travel (maybe 1.5" or so) during taxi and even during a run up, and as i taxi onto the runway i go full rich. Then again after landing as i make the runway turnoff, I'll re-lean the mixture. If you do that, does your engine still run okay?

As for the oil leaks...join the club! Those "accordion" style pushrod covers are okay, but I will always have a small drop of oil leaking out of at least one every time I pull the cowling. If it's a tiny leak and it bothers you, a small dab of red RTV will probably fix it, but if it's a big leak like you're describing the only simple fix I can think of is to remove the head, stretch it back out, and re-compress when you bolt the head back on. Sort of like killing an ant with an AR-15! A call to Kerry on the Sonex tech line may also offer you more clues. Is the tube going straight into the engine case? You can force a little movement out of them if the tube is sitting at an angle; you want them straight against the case.

Sorry I can't help more...hopefully others can chime in some ideas as well.

Good luck and keep us in the loop!

By the way, ask around the shop at your airport and see if anyone has a digital tach you can borrow for a second to make sure your actual RPMs are what you're indicating. Those little digital units are pretty cheap...I bet someone has one.

I tracked down a digital tach and will try next week to see if it is actually putting out only 2750 or if it is some setting with my MGL RDAC or Xtreme. Once I get that figured out I will work on the rest. Slide movement is fine.

At full throttle the motor runs pretty smooth but is really rough at low rpms. I can lean it out but it is almost all the way to the cut off point to get it running smooth down at low rpms.

As for the leak for right now I guess I will just try some red rtv on it and see if it helps. I will prob re-seat them in the near future anyway to see if it helps but it looks like it is a common problem to leak around those tubes.

BTW, I am running 8/1 and using a custom prop that is 54 with a 43 pitch. I am using a K&N filter (brand new and clean) and am at 950ft (not to far from Madison, WI)

With you turning a 43" pitch prop, I'm now even more surprised that you're only turning 2750 rpms. I've heard of a few people custom making a 43" pitch prop to act as more of a climb prop for high elevation altitudes.

I would certainly try a few quick test runs with the needle slightly leaned out to see if that helps any. Let us know how it goes.

Thats why I think it is a setting with my RDAC. I will post my findings next week when I test with an secondary tach.

Who made the prop. I tried several, 43's and 44's. Some props don't have enough "slip" for the Aerovee. My standard Sensenich 54x44 would turn 3180 static but a 54x43Props Inc would only do 2700. You need to be over 3000 to hit the power curve ov the cam.

It is a custom built prop made by a friend who has carved props for many one off planes.

Did you fly behind the Props Inc one? If so how did it perform. Seeing as mine is turning just about 2800 now I think it may be similar performance. Granted I know every one is different but it seems it may be close.

I did fly behind it. It was very fast but no climb rate. The Sensenish that Sonex recommends is a vary thin prop and flattens out under strain. therefore the pitch under strain is a lot less than 44. That's my opinion. I also flew with a Sterba 54x43 and it was great solo but not great at gross although I flew it at 1150 lbs with an AeroVee and saw 300 fpm climb. I was seeing 150 + at 3000 ft Msl. Climb was a little anemic at gross. I think your issue is the prop. If you can send me a picture, I'll make a visual comparison for you. If it has large paddles, that is the problem. I do need to sell the Sterba if you want it.