Do our 2 stroke gas engines tend to lean out in really hot and humid weather conditions?

I have always thought so. Richen the high-end a tiny bit, and verify that you have 3 or 4 times as much exit area as intake area for cooling the engine.

Humid air is less dense than dry air. Moving from a Dry condition to a Humid one is technically 'asking' you to lean the condition. The humid air is harder to pull the airframe through as well, so a hot humid day isn't the day to be over compensating with the needles on a more heavily loaded engine. Moving a properly tuned engine from a humid environment to a dry one, would 'ask' you to richen the condition. Within reason, temperature has less of an affect on my well tuned engines, than moisture does, in the air.

once peaked most will richen the high about the size of a screwdriver blade.

I really notice a difference when flying in the winter. We allways have to richen a CH in winter, not a RCH mind you, but a CH

Sorry, I don't think I understand the terms "CH" and "RCH". Or do I?

Regards,
Richard

warmer or higher or moist: lean out a bit
colder or lower or very dry: richen a bit

Gas engines do lean out very slightly when they get up to working temperature. Not at all like a glow engine though.
Most engines I see flight videos of, are Waaaay to rich.

Right on Pe. Most of the newer gasser folks that show up at our field think you need to run 300 to 500 or more down from peak like you do on glow. This is simply NOT the case, they should be adjusted in the middle of the lean/rich drop point. Properly tuned to start with, I have to readjust EXACTLY as you stated -
warmer or higher or moist: lean out a bit
colder or lower or very dry: richen a bit.

There is logic in that.
It depends on the amount of oxygen in a charge. Oxigen that is used to burn gas. Less oxigen needs leaner settings. (hot, high, moist)
If tuned rich, a gas engine will run only so-so, but once leaned out properly it goes like a scalded dog.

Well the answers have gone both ways. Not much help. Moderator please close the thread.

CH=female pubic hair
BCH=female blonde pubic hair, considered thinner than a CH.
RCH female redhead pubic hair, considered thinner than a BCH

All standard advanced tools of engineering measurement.

I figure this post will last about 30 seconds and I'll likely receive some form of reprimand in the process......

Both ways??
all, except one, said to lean out the engine in warm and humid weather.

Wow Pat!

I thought every one used these standard engineering measurements. Maybe the younger lads haven't been exposed to projects with tolerances requiring those measurements.

Well the fact that you didn't get an exact answer or concensus might be your answer???

While not exactly the same as a full scale four cycle, some characteristics are similar. In a full scale, engine cooling is accomplish with fuel flow, oil flow and air flow. Screw up any of the three and the other two must compensate. So while tooling along at altitude one monitors the engine temps and if they start getting hot, you richen the mixture and/or open the cowl flaps (if equipted) to help cool it off.

Then there's the little tidbit offered by pe about the engines leaning slightly as they warm up. So.... while conventional wisdom would indicate that higher humidity/temps/altitude would indicate that the engine needs to be leaned out, I've found that when the amibient temps get pretty hot/wet, that richening the thing just a tad sometimes works better and we're not talking very much either.

As for Pat's definitions; red hair is the coarsest and about half again the diameter of blond hair so while I'm familiar with your first two definitions for the above acronyms, I've never run into the third one and based on hair diameters it would seem to be the largest ajustment of the three?????

Actually PE, the count is 3 to richen and 3 to lean. So again, MODERATOR, please close the thread.

<hr />Hey Zeeb...are you and TOM related????

You can "take this to the bank." Hot and humid weather makes an engine richen. The air is thinner and you have to lean the engine to compensate if you want optimum mixture setting.

Cool, dry air is more dense, and will lean an engine out. With large temperature changes to cooler air you need to richen your engine to regain optimum mixture.

Barometric pressure and field altitude also make differences. Especially field altitude. An engine loses approximately 3% power for each 1000' increase in density altitude. Density altitude is a function of true altitude, barometric pressure, and temperature. An engine at a density altitude of 7000' will have about 21% less power than the same engine at sea level, 59 degrees, and 29.92 barometric pressure. (ISA) This sounds like a high altitude, but it is commonly encountered in the western United States due to high field elevations and high temperatures. I have seen many 7000' foot days in Tucson, Arizona.

At high density altitudes; over 5000' due to high temperatures and true altitudes, Continental and Lycoming recommend leaning their engines for take off power! In these conditions, you can add full power, and start leaning the mixture on a full size airplane, and just watch the tach start climbing; gaining power because the mixture was too rich. Baseline full rich mixture is set for standard conditions, (ISA) of sea level, 29.92 barometric pressure, and 59 degrees. Any thing above that in temperature, altitude, or lower in barometric pressure, or any combination thereof, causes a richer than optimum setting. Humidity has the effect of lowering air density as well, but is less of an effect than temperature or altitude.

AV8TOR

UHHH..If you actually TUNE your engine before you fly it, what's the difference which way the needles have to be turned ????
Much ado about NOTHING.....LEARN TO TUNE YOUR ENGINE.
NO one can posibly predict what your carb settings willl be....NO book, NO amount of testing, will tell you to open or close your needles every time you fly....AT YOUR ALTITUDE, TEMPERATURE, HUMIDITY, AND PROP SIZE...There is NO chart to look at....
Sheesh, what a STUPID useless discussion....Except the CH part, we learned about that 65 years ago... Even before Pat was born...

Why in the world would you join a "useless" discussion? You must be one of the RCU experts that feels the need to put a rude comment about things they dont agree with. Believe me I know how to tune a gas engine. Was just asking a simple question.

Not quite true Ralf,
The Rotax handbook has graphs on how to lean the settings when you gain altitude.

@ vanguard,
Actually, the count is 5 to lean out, two to richen, two non-conclusive ; make the latter three. Ralf tunes, and forgets

LOL!! You are on a roll today!!

guys read my original post. I didnt ask how to tune an engine. I normally tune them when new and forget them. Hate to mess with needles unless really necessary. Our weather has been very very hot and humid the last two weeks. I noticded that my DA85 started to sag a little after about 10 minutes in the are. Normally sagging would indicate a lean condition. But like others here, i thought the more humid air would richen the mix and would need a slightly lean setting. I chose not to do either as this engine always runs very well. I got in 3 more flights that day and it did sag slightly after 15 minutes in the air the last flight. That was the basis for my question. The DA's I have are all "set it and forget it" engines, thats why I was hesitant to do anything. Its cooling off here next week so I am going to take a look and see attitude. Please Please no more negative comments. I know antigue is a Zenoah expert so his help would have been useful. Enough said, I have contacted the moderator and asked him to end the thread.









guys

You are probably experiencing just the reduced performance effects of the higher density altitude created by the heat and humidity.

Ditto.
Always nice when the OP rephrases.