Aerocarb Alternatives

[bobc170a]

Hi Jeff, Art,
I have read your threads on this Aerocarb tuning and EGT's and found them very informative. I have been only flyning my Sonex Jab powered
just over two years in hot Florida. On my Jab on take off the rear two EGT's will go to 1400. As that happens I throttle back from about 3010
and 8.5 to 9.0 gal per hour to about 2910 to 2930 and the EGT's come down to about 1350. The cylinder temps are usually under 300 where
I want them. Sometimes like yesterday the number 5 cylinder(which is always the hottest) was at 330 degs. The JAb manual states max Cylinder
temp in climb should be 392 and in cruise should be 352 degs.
The higher I go both the ETG's and cylinder temps come down. Now in cruise at 2750 and above 3000 feet I can lean to 6.0 gal and my cylinder temps are below 300 degs and my EGT's are below 1300 which is my goal. I went to a Jab engine seminar with Pete in Dec of 2014 and the class asked him what temps should we see to keep the engine safe. His opinion was always keep the cylinder's below 300 and the EGT's below 1300 in cruise and that is what I have been doing. My Jab idles about 850 when warm and I do not need to lean.

Bob O.

[builderflyer]

David A.,

I thought that I had read that some who had changed out the airfoil shaped splitter for a round one didn't see much of an effect. The time for me to have made the change was a couple of weeks ago when I had the plenum removed for resealing it and the intake tubes. Oh well, next time. Thanks for your report.

BTW, when I removed the plenum I found that there was no Loctite 515 between the two halves. I guess the Jabiru factory made my engine close to quitting time on a Friday.

Art,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,,,,,Jab3300 #261

[builderflyer]

Hi Bob O,

Except for your fuel flow at WOT, your numbers and experience sounds quite similar to mine. The manual for my early 3300, however, calls for a never exceed CHT of 348 F and a max continuous of 302 F and I really work to stick with those limits. In the past, when I let the #5 cylinder CHT approach the limit (it's the hottest on climbout), it displayed signs of overheating so I attempt to keep its CHT below about 320 F or so. Requires a lot of step climbing with a hot engine on a hot day.

Thanks for the info.,

Art,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,Jab3300 #261

[petep]

Interesting that you have good results on the number 3 needle. I started with a #2, it idle fine but the back two cylinders would blow thru 1400 EGT before getting to WOT no matter how much I tweaked the needle. Switched to a 2.5 needle and can get WOT with a 1350 EGT full rich but the idle mixture is all but idle cut off and the engine will die if it is not at that point. Still scratching my head on how to best proceed.
In my YX the Aerocarb tune in beautifully but this guy in the Onex is giving me fits.

[NWade]

Pete -

With the #2 needle was everything OK except the EGT values? If so, then you might be just fine with that needle:
EGT numbers can be misleading and vary a lot from engine to engine (because of small differences in the probes, probe mounting location, etc). I highly recommend watching this Webinar from Mike Busch, a respected A&P who puts on webinars for the EAA and also writes for various aviation magazines. http://www.eaavideo.org/detail/video/13 ... EGT%20myth

And even Kerry Fores of Sonex Aircraft mentioned that EGT numbers should be taken with "a grain of salt" and to watch their "relative values" more than absolute numbers, in his comments on the SonexFlight Podcast Episode #7 (on tuning the AeroInjector) - http://www.sonexflight.com/7/

If you're blowing way past 1400 and the engine is exhibiting signs of running really lean (i.e. no EGT rise when you try to lean the mixture) then you might have a problem; but if the raw EGT number is your only indication and you get the EGT temperature change described in the AeroInjector tuning manual and can run well at WOT with the #2 needle, then you might be just fine and have probes that read a little "hot". Just some things to think about and consider.

Have you called Sonex / Aeroconversions Tech Support and asked them for guidance on the phone? That's always a good option!

Good luck!

--Noel

[sonex1374]

I started with a #2, it idle fine but the back two cylinders would blow thru 1400 EGT before getting to WOT no matter how much I tweaked the needle.

This is a sure sign that the engine was running lean due to a needle thst is too small. To get WOT to a rich enough mixture would require screwing that needle way far out so you were operating right on the tip of the needle (where more material had beed machined away). This isn’t always possible, so the solution is to switch to a larger needle. It’s worth re-emphasizing that the goal is to tune for WOT first, and only when it’s running well WOT do you worry about how it idles. Typically if you have too small a needle the idle will be way too rich, and you’ll know that a larger needle may be warranted.

Switched to a 2.5 needle and can get WOT with a 1350 EGT full rich but the idle mixture is all but idle cut off and the engine will die if it is not at that point. Still scratching my head on how to best proceed.

Again, your situation with the 2.5 needle indicates that a larger needle might help. I would install a #3 and once again tune for WOT. You will likely find that now low throttle runs leaner and better. Idle mixture is a tricky thing, and even with a #3 you may still want to lean a bit at idle, but the larger needle should really help.

Jeff

[petep]

Thanks Jeff. I have already switched to a #3 needle but have not had a chance to start the WOT tuning on the #3. After thinking it over I figured the the steeper slope of the number #3 would help me get the WOT tuned and not be quite as rich at low RPM. Could be wrong but as they say this is experimental!

[Onex107]

[quote="Onex107"]I have 185 hours on my Onex, Aerovee, AeroInjector. The last 100 hours using the #3 needle. I had the same experience as you and others with the #2 and #2 1/2. Great at wot and super rich at idle, requiring a maximum mixture change. We did a significant amount of research, even making a new needle holder and seven needles of our own to solve the problem. As it turned out, #7, unknown to us at the time, was an exact copy of #3. My needles had several problems that made adjustment difficult. First, they were not all the same diameter. Second, the needle holder had too much play in the ball joint. It almost equaled 1/2 turn of adjustment. Third, the wot sweet spot (needle thickness) and the idle sweet spot were not both located within the slide movement, requiring the mixture adjustment.
Tighten up the ball joint any way you can. Try the #3 needle. I have mine adjusted for wot with the mixture about 1/2 inch out. During climb out when temps tend to go high, a small adjustment richer cools things off. Adjusted back to the original setting for cruise. After landing there is no need to touch the mixture, it idles at less than 1000 rpm. I shut down with the main fuel valve so the mixture isn't touched from one flight to the next. It's almost a set and forget.
[Since the above post, I'm at 206 hours and nothing has changed. My mixture stays in the same position, I do not adjust for season change, from 30 degrees to 90 degrees everything stays the same. A small adjustment in mixture, richer or leaner, to keep the EGT's in the same range. Plugs are clean, temps are less than 350 and 1200. The three biggest changes I made were: Eliminate the slop in the needle holder ball joint, use the #3 needle, and change to a larger/better air filter. Fly without one to see if it makes a difference.]

[GWMotley]

Another issue I noted deals with the diameter of the mixture needle orifice. If you do not have a carb with the new white nylon bushing in the mixture orifice, I would suggest contacting Sonex for a possible installation in yours. When I ordered a new carb and this was installed, I had no trouble adjusting the settting. My first carb had about 330 hours on it before difficulty with setting the mixture.

[Darick]

Can anyone with a fuel flow indicator report gph as a definite way to set the carb? For instance what's your gph at wide open throttle?...or at 2000 rpm.

Or is there that much variation in the AeroVee engines that gph will be unique for each engine? It certainly should be some consistancy...enough to get you close.

I have a red cube that so far (only 3 hours) seems to be working good.