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Mixture Useage?

Zazoos

Well Known Member
Need help learning when to use mixture.
I could of sworn Vic said in the EAA Webinar recently that right after startup he leans the engine. However, I was thinking that on the idle circuit of the carb the leaning doesn't really do anything. (I could be and probably am wrong)
Then I read the following:
"The mixture adjustment should not be used under 5000 feet."
Source: Page 8 of MSA Float Carb Handbook located here:
http://www.insightavionics.com/pdf%20files/MA-4%20Carb%20Manual.pdf

While I am on a roll might as well ask one more question.
#1 cylinder EGT consistently runs 150 degrees cooler than the other 3. Generally is right at 1200 degrees and the others are near 1350. CHTs are all close to the same. Should I be concerned about the low EGT on #1 cylinder?

Thank you for the help.
 
I lean my carburetor very aggressively after start, probably 3/4th of the way out. It will be very rich if you dont.
 
On the ground

Lean very aggressively after engine start and during taxi, then go to full rich for the take off and climb, usually to about 5000 feet or higher. Then lean as desired.

Some folks like to lean on the climb but it is more risky to the engine unless you have CHT/EGT gauges for all cylinders and understand how much lean can safely be tolerated.
 
EGTs

EGT temps may or may not run at the same temps, lots of variables. On a carb engine, airflow varies at different RPMs, EGT probs are sometime not exactly the same distance down the pipe from the exhaust port exit, intake leak in one of the intake pipes...

Any of these items might cause a difference in EGT numbers between cylinders.

Probably should have an A&P look at it if you're really concerned, however from what was posted it doesn't sound to serious.
 
"I was thinking that on the idle circuit of the carb the leaning doesn't really do anything."

Don't you shut the engine down from idle by pulling the mixture back???

"The mixture adjustment should not be used under 5000 feet."
This is for in flt, when you are at high power settings.

Lean aggressively on the gnd and when you forget to push it back up on taking the rwy, you will be reminded to as the eng will quit.
 
Leaning... the subject is almost as old as flying itself :)

Forget the 5000 ft, old wives tales. Lean to your heart?s content if below 75% power. Could be at 2000ft...
For this either read your % power display, or consult the manufacturer power tables, or use Jim Pettys excellent and free iOS app AircraftPower.
 
The definitive guide to engine leaning (and lots of other useful information) may be found here:
Sadly, all of Deakin's articles have been pulled. All I get is "Error 404".

I fly out of a 2,100' airport and lean about 1" for the mag check. This technique is approved by Lycoming.

On a 90F day, I lean maybe 2" as I start my takeoff roll. Otherwise, my engine will sputter and even quit due to being too rich. As I pick up speed, I slowly push the mixture control back in.
 
I lean my carburetor very aggressively after start, probably 3/4th of the way out. It will be very rich if you dont.

Idle mixture is controlled by the idle mixture circuit, with a unique adjustment, and should require no manual leaning if set up correctly. This is good to about 1000 RPM. Higher than that and you are slowly transitioning to the main circuit. However, it is not obscenly rich in that transition zone, like it is at higher RPMs.

For those that have adjusted their idle mixture via the EGT rise method, they have seen exactly how much effort it takes to precisely lean the mixture via the red knob at idle. Once it begins to take effect, it is very little movement before it is too lean and stops running. Simply pulling the red knob back to some arbitrary location is simply a placebo. I have never leaned on the ground and in 600 hours never fouled a plug or had ill effects from mixture; both with a carb and FI.

an engine running at anything but a constant RPM/power load MUST have a variable mixture control (basic function of a carb/FI servo). The red knob is an absolute flow metering override mechanism (it sets the max flow that the variable mechanism can use) and can only be used effectively at constant power/rpm modes. The absolute flow set for 1400 RPM, will be rich at 1300 (variable mixture control is in charge here) and start choking at 1500. If you are able to taxi with variable power settings, your red knob setting is not doing anything across the bulk of the RPM range.


Larry
 
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Idle mixture is controlled by the idle mixture circuit, with a unique adjustment, and should require no manual leaning if set up correctly. This is good to about 1000 RPM. Higher than that and you are slowly transitioning to the main circuit. However, it is not obscenly rich in that transition zone, like it is at higher RPMs.

For those that have adjusted their idle mixture via the EGT rise method, they have seen exactly how much effort it takes to precisely lean the mixture via the red knob at idle. Once it begins to take effect, it is very little movement before it is too lean and stops running. Simply pulling the red knob back to some arbitrary location is simply a placebo. I have never leaned on the ground and in 600 hours never fouled a plug or had ill effects from mixture; both with a carb and FI.

an engine running at anything but a constant RPM/power load MUST have a variable mixture control (basic function of a carb/FI servo). The red knob is an absolute flow metering override mechanism (it sets the max flow that the variable mechanism can use) and can only be used effectively at constant power/rpm modes. The absolute flow set for 1400 RPM, will be rich at 1300 (variable mixture control is in charge here) and start choking at 1500. If you are able to taxi with variable power settings, your red knob setting is not doing anything across the bulk of the RPM range.


Larry
I’m definitely not an expert, and I’m not fully sure that you are arguing against leaning on the ground as a general rule, but if so Mike Busch definitely appears to disagree. See first 10 minutes or so of his “Leaning Basics” video...

https://m.youtube.com/watch?v=_VfiPuheeGw
 
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I’m definitely not an expert, and I’m not fully sure that you are arguing against leaning on the ground as a general rule, but if so Mike Busch definitely appears to disagree. See first 10 minutes or so of his “Leaning Basics” video...

https://m.youtube.com/watch?v=_VfiPuheeGw

I am very comfortable with the intricacies of how a carb/FI works and am not overly interested in Mike's opinion on the subject or whether my understanding meshes with his. Just trying to throw out some facts so that folks can educate themselves and make informed decisions instead of simply accepting old wives tales and misinformation.

I was not really trying to argue one point or another. I did that once and was attacked. Mostly arguing the notion stated by a poster that you will be too rich at idle if you don't pull the red knob to 3/4 out; That is simply wrong. If anyone every looked at the complexity of an EFI fuel map, they would understand that one cannot set fuel mixture or lean with something as crude as the red mixture knob in anything but static conditions. And this is completely unnecessary at idle, as there is a uniquely adjustable idle mixture circuit just for that purpose on the carb/FI servo independant of the red knob.

Larry
 
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I'm in full agreement with Larry that an arbitrary pull of the mixture a certain distance does not achieve a whole lot as things are so variable from aircraft to aircraft. That said I think the easiest thing to do in this situation is resort to the manufacturers recommendations, which seem to reflect those of Mike Busch, John Deakin and the 1 second interval data from my G3X fuel flow readings at typical taxi RPM's where the mixture control has a clear impact on fuel flow and subsequent air/fuel mixture.

The following is an excerpt from the IO-360 L2A operations manual:

"Ground Operation and Engine Shut Down
1. If an extended taxi is likely, make the fuel mixture Lean to Best Power during taxi.
Leaning Technique
a. Slowly make the fuel mixture Lean until the RPM decreases.
b. Make the fuel mixture Rich until the engine operates smoothly. "

https://www.lycoming.com/sites/default/files/Engine Procedures for Flight Training Operations.pdf

Doesn't get much more clear cut than that.

No point squirting unburnt fuel out your tailpipe if you don't need to, although hopefully all these discussions will evaporate like the unburnt fuel in a couple of years when we shift to battery electric.

If I get a chance tomorrow I will gather some one second data during ground ops in the leaned and rich condition.

Tom.
RV-7 IO-360M1B
 
The lead in the avgas doesn't really burn off until it reaches around 1000 degrees F. Take a look at your EGT's when you are taxiing. They are usually much lower than that. So the idea is to put as little fuel as possible into the cylinders.
The alternative is to run the engine at a higher RPM, but that just burns up the brakes.

We see about 6 or more airplanes per week through the shop, so a good bit of data here across 7-8 years. When I see plugs that are full of lead I ask if they are leaning on the ground. Invariably, the answer is no.

Yes, you could take the time to set up your system so it is perfectly leaned on the ground and requires no further pull on the red knob. Guess what? That works for one altitude and one temperature. Anything other than that and the mixture is no longer perfect. Perhaps that is why we lean for high altitude takeoffs?

I fly almost every day in the RV-10. Sometimes it is below freezing in the morning and mid 60's in the afternoon. I do see a difference in the position of the red knob from morning to afternoon.

I'm not trying to say I'm right and everyone else is wrong. I'm just trying to share expereince with you so you don't end up on that vacation trip with a fouled plug when it is time to leave.

Vic
 
The lead in the avgas doesn't really burn off until it reaches around 1000 degrees F. Take a look at your EGT's when you are taxiing. They are usually much lower than that. So the idea is to put as little fuel as possible into the cylinders.
The alternative is to run the engine at a higher RPM, but that just burns up the brakes.

We see about 6 or more airplanes per week through the shop, so a good bit of data here across 7-8 years. When I see plugs that are full of lead I ask if they are leaning on the ground. Invariably, the answer is no.

Yes, you could take the time to set up your system so it is perfectly leaned on the ground and requires no further pull on the red knob. Guess what? That works for one altitude and one temperature. Anything other than that and the mixture is no longer perfect. Perhaps that is why we lean for high altitude takeoffs?

I fly almost every day in the RV-10. Sometimes it is below freezing in the morning and mid 60's in the afternoon. I do see a difference in the position of the red knob from morning to afternoon.

I'm not trying to say I'm right and everyone else is wrong. I'm just trying to share expereince with you so you don't end up on that vacation trip with a fouled plug when it is time to leave.

Vic

To add on to Vic's post: The standard lycoming procedure of setting the idle mixture to achieve a 50 RPM rise when leaning to idle cutoff during idle is essentially a rich mixture and is designed to give a good positive engine response when advancing the throttle from idle such as during a go-around or a touch and go. When the idle mixture is set much leaner, you will often get a stutter or hiccup in these situations. However, for steady state ground operation, this is a bit richer than needed and can cause some lead and carbon build up in the cylinders. Hence the reason that folks like John Deakin and Mike Bush recommend aggressive leaning on the ground.

Skylor
RV-8
 
We see about 6 or more airplanes per week through the shop, so a good bit of data here across 7-8 years. When I see plugs that are full of lead I ask if they are leaning on the ground. Invariably, the answer is no.

Vic

I don?t know how people that don?t lean on the ground get through a mag check. If I don?t lean aggressively, either after landing or taxing out for takeoff, my mag check will run rough. I then need to pull the red knob and run a few seconds for it to clear the plug/plugs. My mixture was set for 50 rpm rise on a day when it was 60 degrees and as Vic said, that is good for only 60. All other temps I get rough running mag checks when/if not using mixture knob during taxi.
 
I don?t know how people that don?t lean on the ground get through a mag check. If I don?t lean aggressively, either after landing or taxing out for takeoff, my mag check will run rough. I then need to pull the red knob and run a few seconds for it to clear the plug/plugs. My mixture was set for 50 rpm rise on a day when it was 60 degrees and as Vic said, that is good for only 60. All other temps I get rough running mag checks when/if not using mixture knob during taxi.

Dead on, Phillip. It is especially noticeable if you have both an electronic ignition and a mag on the same engine. The electronic ignition is much more efficient at burning the fuel. By now you will have noticed that you get much less of a drop on the electronic ignition. Play with the mixture when checking the magneto side and you will notice that the mag requires a different mixture setting for an optimal check.

Vic
 
I don’t know how people that don’t lean on the ground get through a mag check. If I don’t lean aggressively, either after landing or taxing out for takeoff, my mag check will run rough. I then need to pull the red knob and run a few seconds for it to clear the plug/plugs. My mixture was set for 50 rpm rise on a day when it was 60 degrees and as Vic said, that is good for only 60. All other temps I get rough running mag checks when/if not using mixture knob during taxi.

Must be something different in routines or other variables. As I mentioned, I have my idle mixture properly set (best MAP method) and treat my engine in a thoughtfull manner. At 640 hours, I have never fouled a plug or had any cyl not get an EGT rise at runup (i.e. all plugs firing). I have never attempted to lean during ground operations via my red knob. I routinely run up my engine to 1800 for a few seconds before shut down, as well. I have one mag and one EI. I do use 37BY plugs that are more resistant to lead collection.

If you must lean on the ground, I would suspect your idle mixture may be too rich. As I mentioned, if you use the red knob to lean your idle to something around 13.5 AFR, you will be unable to advance throttle more than a couple hundred RPM before it starts coughing. Pretty tough to taxi at 8-900 RPM. Much better to get the idle mixture right and use the mechanisms designed for this purpose.

For those wanting to better understand this, do a test. At idle, pull the red knob back until you get some (25-50) EGT rise. You have now actually leaned the idle mixture with the red knob. Now advance the throttle and try to taxi. See what happens. If you have effectively leaned your idle, you will not be able to advance the throttle enough to begin to roll.

Larry
 
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I routinely run up my engine to 1800 for a few seconds before shut down, as well. I have one mag and one EI. I do use 37BY plugs that are more resistant to lead collection.Larry

Running up as you do prior to shutdown is a best practice, and along with the use of REM37BY plugs, is a huge contributor to why you don't have lead fouling.

You should be able to taxi with the mixture leaned on the ground; however, you will not be able to apply take-off power.

Vic
 
At 640 hours, I have never fouled a plug or had any cyl not get an EGT rise at runup (i.e. all plugs firing). I have never attempted to lean during ground operations via my red knob. I routinely run up my engine to 1800 for a few seconds before shut down, as well. I have one mag and one EI. I do use 37BY plugs that are more resistant to lead collection.

In 860 hours I have also never failed a mag check on my plane with 2 Slick mags. I DO NOT do a run up pre-shut down which tends to annoy some hangar neighbors. I lean during ground ops.

Skylor
 
Is this to remove lead? The Rotax engines I fly recommend this, but I've never done it on a Lycoming.

Yes, works great on Lycoming's too. As I mentioned in an earlier thread, it raises the temps in the combustion chamber and helps to get rid of the lead. Also, Lycomings are a "splash lubricated" engine, so it helps to get some oil back up on some of those moving parts.

Vic
 
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