carb mixture adjustment questions

Hi all,

I think my carbs may have slightly different mixtures, and that leads me to a couple of questions. Background: I had a very hard time getting the engine to run smoothly on initial installation. My A&P did adjust the mixture on the right in the process of balancing the carbs.

1) Is a consistent 50 ?F difference between EGT's significant?

2). With respect to the Maint Man pg 12-12, what is "a turn"? Is it 180? or 360? of rotation?

3) If the 50 ?F difference is significant, then is adjusting the leaner (right) carburetor appropriate, and by how much?

thanks in advance,

David,

I was about to say what Mike said and will add regarding the EGT differences ? did you first make sure the main jet in the bowl is turned 1 ? turns open from fully closed for both carbs?

Also, when balancing the carbs, I followed the suggestion of using a higher RPM of over 3,000 (think I used 3,500) when doing the off idle balance adjustment. This insures you are out of the low speed circuit in the carbs and running on the high speed circuit. My engine runs very smooth now.

The difference you are seeing in EGT temps could also be from a difference in the EGT probes. This can easily be checked by flip flopping the EGT probes and taking stock of the results. This way you will know if there is an actual EGT difference or if one of the probes reads a little off.

Based on a data sheet that Leading Edge has, the normal EGT range for the Rotax 912ULS is around 1,472 degrees F ?. the maximum limit is 1,652.
Once you have determined the probes are fairly accurate, I would be looking at where the actual EGT temps are ? if they are much lower than 1,472 degrees you are likely running with a rich mixture and if the EGT temps are way above 1,472 degrees you are likely running leaner than desirable.

Happy Flying,

My EGT readings - -



A little faster than I usually cruise. About 66 degrees OAT. This is about normal for mine.

I don't know that I have ever seen EGT readings above 1250 or so in my RV-12. They're usually around 1180 - 1220. The biggest different L to R that I have seen was a little under 50 degrees, they're usually within +/- 25 of each other.

I?m guessing the EGT temperatures from the Leading Edge data sheet I was quoting from likely reflect full power temperatures and not EGT?s at cruise.

I routinely see EGT temps in the 1,440 - 1,475 degree range during a full power climb out to pattern altitude. That said, I?ve just recently begun phase one testing and have yet to do any long continuous full power climb-outs where, I?m guessing, the EGT temperatures will likely go well beyond 1,475 degree mark.

According to "The Savvy Aviator", Mike Bush, There is no limit for EGT. The main concern is high CHT.
My EGT temperatures are usually around 1350.

Im sure you mean EGT, not CHT at 1300+ degrees.

Yes, EGT. Fixed it.