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Let's talk engine leaning on the ground.

jcarne

Well Known Member
Patron
Okay, we all know that engine leaning on the ground is mega important to avoid deposit build up when running 100LL. How aggressive is aggressive?

I have heard many people say "lean until it's rough and then just rich enough to smooth it out". This leads me to a question.

When I lean my engine on the ground this is what it looks like in order as I bring the mixture back:
1. engine rpm increases
2. RPM maxes. At throttle back all the way engine rpm will be up around 950-1000 RPM (These numbers are off, correct ones are in post 12)
3. I can continue to lean without much changing for a little bit
4. The engine starts to develop a ticking sound and EGT on #3 starts rapidly going up compared to the others
5. RPM starts dropping and engine starts running rough

So here are my questions. What the heck is that ticking sound coming from? Should I richen enough to make it past the ticking sound or just rich enough to avoid the rough running?
 
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Okay, we all know that engine leaning on the ground is mega important to avoid deposit build up when running 100LL. How aggressive is aggressive?

I have heard many people say "lean until it's rough and then just rich enough to smooth it out". This leads me to a question.

When I lean my engine on the ground this is what it looks like in order as I bring the mixture back:
1. engine rpm increases
2. RPM maxes. At throttle back all the way engine rpm will be up around 950-1000 RPM
3. I can continue to lean without much changing for a little bit
4. The engine starts to develop a ticking sound and EGT on #3 starts rapidly going up compared to the others
5. RPM starts dropping and engine starts running rough

So here are my questions. What the heck is that ticking sound coming from? Should I richen enough to make it past the ticking sound or just rich enough to avoid the rough running?
I don’t know what the ticking sound is but the other symptoms you describe indicate that your idle mixture and idle speed stop screw are not properly adjusted. It sounds like your idol mixture is way too rich. Adjusting that properly will allow you to adjust the idle speed screw for a lower speed.
 
I don’t know what the ticking sound is but the other symptoms you describe indicate that your idle mixture and idle speed stop screw are not properly adjusted. It sounds like your idol mixture is way too rich. Adjusting that properly will allow you to adjust the idle speed screw for a lower speed.

You may be right Scott but just to clarify: when not aggressively leaned it idles around 750 RPM. (which thinking on it now may confirm what you said) The lowest idle only goes up when aggressively leaned. Perhaps I need to do the shut down rise test some more and play with the mixture screw some more (I leaned it a few clicks but it's been awhile).
 
What DA range is an idle setting good for?

Do what Scott says.

But there may be more consideration for your climate. My YIO360M1B first flight was in Jan (18) so it was cold. Only 15F but cold. Power application was like an old 2-stroke dirt bike with a pipe. Stumbled with throttle advance until it got off the idle circuit (xx rpm) and blasted off. DA was -3500' or so.

I set idle mix with 50 rpm rise via slow extraction of mix when cold and when warmer weather arrives it is too rich. To compensate, I start engine and pull mix about 3/4" (YMMV) when on ground or the sniffle valve will spit all over the fuse.

Edit: You need to determine what that ticking is. It could be anything - maybe something loose. I have heard loose spark plugs tick.
 
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At your 4200 ft elevation you'll want to be careful not to go too lean or it may not idle at sea level.

Ticking sound. Might be worth checking for an exhaust leak especially at the exhaust port flange. Without hearing it, it is impossible to say, it may be more noticeable when leaning.
 
I am in the camp that if the idle mixture is set correctly there is no need to lean with the red knob on the ground. I'll spare you the rationale, but I have 750 hours on the 6 and `175 on the 10 and have never had a plug fouling that prevented a spark and I have never attempted to lean on the ground. Maybe a couple of tiny balls to pick out when I gap the plugs, but never a missing spark event. I use 37BY's and auto plugs. I also run up to 1800 briefly before shut down. At 750 hours, cylinders and are nice and clean and valves look great.

Agree with other that ticking should be identified and I certainly would keep it rich enough to avoid the ticking.

Larry
 
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At your 4200 ft elevation you'll want to be careful not to go too lean or it may not idle at sea level.

Ticking sound. Might be worth checking for an exhaust leak especially at the exhaust port flange. Without hearing it, it is impossible to say, it may be more noticeable when leaning.

+1

bad exh flange gaskets can create popping in the exh at idle RPMs and much worse on decelleration. Also, afterfires can occur in the exh when you get too lean on a cyl.. Given all the noise in our planes, possibly you are mistaking these pops/explosions for ticking.
 
Next time

Next time you hear the ticking sound, see if it is in sync with a prop blade passing by. I think it might be after fire since it coincides with an egt rise. JMHO.
 
I just lean on the ground with a quick pull far enough that the plane would complain if I tried to take off without enriching. It’s about an inch back on my red knob.

I used to fly a Cessna 172 and it would get fouled plugs during taxi if I neglected to lean. They would show up as a very rough mag check and could be fixed by doing a lengthy high power run up. We would also see lead deposits in the spark plugs.

David
 
I have an airflow performance fm200 and pmags, and I can idle at about 680 rpm and can lean until it just stops, and I normally idle around 800 rpm when warming up the oil. No ticking. I'm running unleaded avgas (UL91) so leaning is probably not that helpful.

What are your EGTs and FF doing when leaning?
 
Okay just got back from flying and the numbers I gave you all in the first post were really off. I must of had my friction lock set just tight enough that I sometimes couldn't get it to its true idle. IDK why but 1000 RPM was stuck in my head. Here are the real numbers.

Idle full rich was about 820 and then I could quickly twist to lean it to about 900 before it very very rapidly fell off, a little more fuel and it maintained 850. If I leaned on the ground like I normally do (I usually do this around 1000 RPM) I could then go to idle around 850.

So it would appear that the mixture is set right, maybe slightly rich still. Thoughts? I'm not the only one slightly confused on this because the manual says "smooth pull" on the mixture knob but gives no indication what so ever how fast the pull is supposed to be when checking the RPM rise. In case you are wondering DA was 4000' and engine was warm after flying for an hour.

My idle could probably be a tad lower but it's never been a problem.
 
+1

bad exh flange gaskets can create popping in the exh at idle RPMs and much worse on decelleration. Also, afterfires can occur in the exh when you get too lean on a cyl.. Given all the noise in our planes, possibly you are mistaking these pops/explosions for ticking.

Next time you hear the ticking sound, see if it is in sync with a prop blade passing by. I think it might be after fire since it coincides with an egt rise. JMHO.

I think you guys are spot on the money. The "ticking" always starts when the #3 EGT starts its rapid rise compared to the rest. My ears are not nearly as trained as others but it sure does make sense that the sound I'm hearing is from after-fires from being very lean. (ticking probably wasn't the best wording) If you look at the data above you can see when I lean #3 EGT really heads on up, this would also support the theory.

Every time I have the cowl off I inspect everything thoroughly, I have never found a loose spark plug, leaking spark plug, leaking exhaust gasket, or loose exhaust nuts.
 
What is your engine/prop configuration? Assume carbureted from the comments? Fixed or CS prop?

Your idle sounds high to me. And if your Idle RPM starts changing as soon as you move the mixture knob out of full rich, somethings not right.

A complete description of your engine installation might help.
 
What is your engine/prop configuration? Assume carbureted from the comments? Fixed or CS prop?

Your idle sounds high to me. And if your Idle RPM starts changing as soon as you move the mixture knob out of full rich, somethings not right.

A complete description of your engine installation might help.

IO-360-M1B with Hartzell CS. Ignition is one Pmag and one Slick. The RPM does not start changing right when mixture is leaned, there is a band in there where it doesn't do anything to RPM. Yes idle may be a bit high but that is an easy fix and to be honest I have never had a problem during flying with that idle setting.
 
Thanks for the update. High idle is not a big deal if you have a CS prop, which idles at flat pitch.
But it's a different story if you have a fixed pitch prop. A high idle causes excess thrust at idle, and makes your landing rollout longer, sometimes significantly.
On my FP plane, I try to keep the closed-throttle idle at or below 500. The resulting idle isn't pretty, a bit rough and lumpy. But when landing, closing the throttle doesn't result in 500 RPM due to the forward airspeed.
Sorry for the thread drift.
 
Thanks for the update. High idle is not a big deal if you have a CS prop, which idles at flat pitch.
But it's a different story if you have a fixed pitch prop. A high idle causes excess thrust at idle, and makes your landing rollout longer, sometimes significantly.
On my FP plane, I try to keep the closed-throttle idle at or below 500. The resulting idle isn't pretty, a bit rough and lumpy. But when landing, closing the throttle doesn't result in 500 RPM due to the forward airspeed.
Sorry for the thread drift.

No worries, I always appreciate the knowledge of others! I have heard of people really working to get their idle speeds down and for a FP it makes sense. You are correct, with the CS prop it drops in nicely with little float; at least that is what my experience thus far has shown. Almost at 70 hours now with the current setting. I tried before my first flight a few months ago to get the idle lower but I just wasn't happy with how it ran down in the 650 range. (seems to be the magic number most people on VAF shoot for haha)
 
Sea level mixture

For those of us not quite up on the engine settings...
Don't you need the mixture rich enough to be correct at sea level?
Seems like if you adjust it perfect for altitude, your engine is lean at a sea level airport.
Maybe I don't understand the discussion.
 
I tried before my first flight a few months ago to get the idle lower but I just wasn't happy with how it ran down in the 650 range.

Jereme,

Lycoming calls for the idle rpm adjustment to be done with the engine thoroughly warmed up. You might not have been thoroughly warmed up while on the ground before your first flight. I recommend that this adjustment be done shortly after landing. Your engine might idle much smoother at a lower rpm now that you have some hours on it.

Since these engines don't have a choke or other enrichment device, Lycoming specifies a rich idle setting so the engine will idle when cold. When warmed up, the mixture is a bit rich. That's why the idle rpm increases when leaning after the engine is completely warmed up.

Attn Larry Larson: If the idle mixture adjustment is done at altitude, I'd expect it to be lean at sea level. In this case, I'd adjust for a more that 50 rpm rise when setting the idle mixture. Don't ask me how much more. You'd have to adjust your own airplane at sea level, and then check the rpm rise when you get back home. If you adjust for a more than 50 rpm rise at altitude, that's all the more reason to lean while on the ground.

Informed and polite rebuttal welcomed.
 
For those of us not quite up on the engine settings...
Don't you need the mixture rich enough to be correct at sea level?
Seems like if you adjust it perfect for altitude, your engine is lean at a sea level airport.
Maybe I don't understand the discussion.

I think you understand correctly.

The original discussion was how much do others lean on the ground. It morphed into idle mixture talks, mainly because my original numbers were not accurate.

I still don’t know if others can lean it enough for the sound to change due to after fire like mine does. All the signs point to this. Guess I’ll just lean until I hear it and then richen until I don’t.
 
"The original discussion was how much do others lean on the ground. It morphed into idle mixture talks." Jereme

Yes, it did morph.

I pull the mixture on the ground until three fingers will fit between the mixture knob and the nut on the instrument panel. Have to richen quite a bit to get a good mag check, and richen again for takeoff.

Field elevation - 4234' O-360-A1A
 
It sounds like most of these comments relate to fuel injected engines. When I had my fuel injected RV8 I could see the reduction in fuel flow when leaning on the ground. On my carbureted fixed pitch RV4, leaning on the ground doesn’t appear to do anything until I get in the idle cutoff range. Fuel flow indication stays the same. Is that because my carb is operating on an idle jet, and it is not affected by mixture adjustments in that range?
 
It sounds like most of these comments relate to fuel injected engines. When I had my fuel injected RV8 I could see the reduction in fuel flow when leaning on the ground. On my carbureted fixed pitch RV4, leaning on the ground doesn’t appear to do anything until I get in the idle cutoff range. Fuel flow indication stays the same. Is that because my carb is operating on an idle jet, and it is not affected by mixture adjustments in that range?

the gross mixture control on a carb is different than a servo. It is the first thing the fuel sees as it goes from the bowl. It is a simple rotary valve arrangement and it is not somewhat variable and tied to fuel flow, like an FI servo is. Leaning with the red knob (i.e. the valve mentioned) does nothing until the size of that valve becomes as small as the jet(s) that fuel is flowing through. If you use the knob to lean at 1000 RPM fuel flow, the setting will do nothing to lean at the 800 RPM fuel flow and will get very lean and rough by 1200. This is why it is futile to try leaning with the red knob on the ground, where changing RPMs is the norm. Just get your idle mixture set properly and let the carb do the leaning. The fuel flow is metered mostly by the idle jet untill around 1200 RPM. Therefore, the best way to avoid fouling is to have your idle mixture set correctly. I use the highest vacuum / lowest MAP method (engine fully warmed up) when temps are 50 degrees. This is about the middle of the temp ranges that I see and temps will affect the optimal mixture. TO the others, using this method, I have no problems idling when visiting Denver (I am based at 800 MSL), with DAs as high as 11K.
 
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I live at 4,000 elevation with DA's over 8K in the Summer. If you leave either a carbureted or FI engine full rich for takeoff here you might go through the bushes at the end of the runway. We have seen many aircraft on the performance level of a Cessna 172 stop for fuel in the Summer and top their tanks and follow the POH and use full mixture for takeoff. This often results in the pilot having dirty underware whether or not they make it into the air. Student pilots here are taught to optimize mixture during run up and it is only on very cool Winter days that the mixture will be anywhere near full rich for takeoff. I see northern flatlanders here posting about never leaning on the ground which is fine for their local conditions. But in the intermountain West we only start on full rich and lean for taxi and then enrichen for runup where we then optimize the mixture prior to takeoff. And I have flown with visitors not used to this and I am amazed how often it freaks them out to optimize mixture during run-up. Idle mixture doesn't enter the picture if adjusted for appropriate RPM roll when pulled to idle cut-off.
 
I live at 4,000 elevation with DA's over 8K in the Summer. If you leave either a carbureted or FI engine full rich for takeoff here you might go through the bushes at the end of the runway. We have seen many aircraft on the performance level of a Cessna 172 stop for fuel in the Summer and top their tanks and follow the POH and use full mixture for takeoff. This often results in the pilot having dirty underware whether or not they make it into the air. Student pilots here are taught to optimize mixture during run up and it is only on very cool Winter days that the mixture will be anywhere near full rich for takeoff. I see northern flatlanders here posting about never leaning on the ground which is fine for their local conditions. But in the intermountain West we only start on full rich and lean for taxi and then enrichen for runup where we then optimize the mixture prior to takeoff. And I have flown with visitors not used to this and I am amazed how often it freaks them out to optimize mixture during run-up. Idle mixture doesn't enter the picture if adjusted for appropriate RPM roll when pulled to idle cut-off.

Good point. I only meant not leaning if for taxi and idle. Mixture adjustment for high density altitude takeoff is still necessary.
 
Thank you Larry. That makes sense. I’ll leave the mixture rich on the ground.

And to be clear, I leave mixture rich on the ground because I have a properly adjusted Idle mixture. Without getting that optimized, leaning on the ground may be necessary to prevent plug fouling. I only advocate full rich on ground IF the idle mixture is properly sorted out.

I also agree with the above about high altitude op's. When I speak of full rich on the ground, I am referring to taxi, NOT take off. Whenever I visit denver, I always lean during a runup and carefully watch EGTs on initial roll out to optimize mixture settings. I know my engine and know what EGT to expect at 2700 and lean to that number on the roll if not there already. This is a bit easier with FI than a carb.
 
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And to be clear, I leave mixture rich on the ground because I have a properly adjusted Idle mixture. Without getting that optimized, leaning on the ground may be necessary to prevent plug fouling. I only advocate full rich on ground IF the idle mixture is properly sorted out.

I also agree with the above about high altitude op's. When I speak of full rich on the ground, I am referring to taxi, NOT take off. Whenever I visit denver, I always lean during a runup and carefully watch EGTs on initial roll out to optimize mixture settings.

I suggest the old school method.

If you have idle mixture perfectly set (as I do) you know this by the ~50 RPM rise as you move the mixture control to cutout. At full rich idle you are still much richer than the engine needs to keep running. The low CHT and excess fuel then become a problem - for things like fouled plugs.

Lean the engine on the ground until just before it stops. If you then add throttle to taxi and the engine bogs, you are just lean enough. Add a little mixture if you need to taxi faster.

The engine power is so low you cannot lean it too much.

Carl
 
I suggest the old school method.

If you have idle mixture perfectly set (as I do) you know this by the ~50 RPM rise as you move the mixture control to cutout. At full rich idle you are still much richer than the engine needs to keep running. The low CHT and excess fuel then become a problem - for things like fouled plugs.

Lean the engine on the ground until just before it stops. If you then add throttle to taxi and the engine bogs, you are just lean enough. Add a little mixture if you need to taxi faster.

The engine power is so low you cannot lean it too much.

Carl


Well said Carl. This is the correct method for leaning your engine on the ground. Copy and paste this into your POH.
 
I suggest the old school method.

If you have idle mixture perfectly set (as I do) you know this by the ~50 RPM rise as you move the mixture control to cutout. At full rich idle you are still much richer than the engine needs to keep running. The low CHT and excess fuel then become a problem - for things like fouled plugs.

Lean the engine on the ground until just before it stops. If you then add throttle to taxi and the engine bogs, you are just lean enough. Add a little mixture if you need to taxi faster.

The engine power is so low you cannot lean it too much.

Carl

Carl I believe you have Pmags on your setup. When leaned far enough do you hear any sound change in the engine? Like I mentioned I hear a bit of after fire in mine (as we pin pointed in this thread). Mine goes from max RPM to sound change to about to quit. The sound change is pretty subtle but it's there if I get it very very lean.
 
Carl I believe you have Pmags on your setup. When leaned far enough do you hear any sound change in the engine? Like I mentioned I hear a bit of after fire in mine (as we pin pointed in this thread). Mine goes from max RPM to sound change to about to quit. The sound change is pretty subtle but it's there if I get it very very lean.

The short answer is no.

I assume you have the pMags timed correctly (25BTDC parallel valve, 20BTDC angle head).

Carl
 
Could the sound you hear be mechanical like the fuel pump push rod or similar? Or possibly something rubbing or tapping something else (exhaust? Air intake? other?) as the engine gets progressively rough with leaning?
 
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The short answer is no.

I assume you have the pMags timed correctly (25BTDC parallel valve, 20BTDC angle head).

Carl

I have one Pmag that is timed about 1-2 ATDC as per the manual. (parallel valve) The slick is spot on 25 BTDC. At least it was when I set it there. Next time I have my cowl off I will check timing to see if it has drifted at all. I checked the timing on the Pmag about 10 hours ago and it hadn't changed.

I also switched to ANR headsets about 20-30 hours ago so everything sounds a little different now...
 
Could the sound you hear be mechanical like the fuel pump push rod? Or possibly something rubbing or tapping something else (exhaust? Air intake? other?) as the engine gets progressively rough with leaning?

I suppose it's possible but I have never found any signs of rubbing on any of my inspections. No abnormal metal in the filter/screen, and a pretty dang good oil analysis.

The sound is also perfectly in sink with when the EGT on #3 starts it's rapid climb while leaning which indicates to me that it is just the afterfire effect.

I'm guessing it is benign but it still bugs me to not know what it is.
 
And to be clear, I leave mixture rich on the ground because I have a properly adjusted Idle mixture. Without getting that optimized, leaning on the ground may be necessary to prevent plug fouling. I only advocate full rich on ground IF the idle mixture is properly sorted out.

I also agree with the above about high altitude op's. When I speak of full rich on the ground, I am referring to taxi, NOT take off. Whenever I visit denver, I always lean during a runup and carefully watch EGTs on initial roll out to optimize mixture settings. I know my engine and know what EGT to expect at 2700 and lean to that number on the roll if not there already. This is a bit easier with FI than a carb.

I have a hard time believing your idle mixture is so perfect that your engine wouldn't benefit from leaning on the ground. If your always preheating your engine to 200ish degrees and thats the temp you adjusted the idle mixture at I could maybe find some truth in it but that seems like a strech.

Every engine needs a touch more gas to run smooth when there cold. Id really like you to lean the mixture when your idling the engine the next time your getting ready for a flight and see if you get an EGT rise.

It's best to have some leeway adjusted into the mixture for changes in ambient temps and elevations.

I can tell you on my IO-360 I have the idle mixture down to less than a 10RPM rise approaching cutoff But, If I idle at 900RPM during a warmup and lean it out I can raise my EGT's from 1000 to 1200.

My carbed 0-320 in the cherokee was the same also.
 
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Ticking sound

If the sound of the ticking ( clicking and pinging) correlates with the elevated temperature of one cylinder, my suspicion would be differential expansion of the exhuast pipes . Perhaps a slip joint is too tight or a hanger bracket is binding.

Kinda like old cars and trucks of the 70's cut them off when they were really hot you could hear them ticking , pinging, and clicking for quite a while as they cooled down.
 
"Perfect" Mixture

I suggest the old school method.

If you have idle mixture perfectly set (as I do) you know this by the ~50 RPM rise as you move the mixture control to cutout. At full rich idle you are still much richer than the engine needs to keep running. The low CHT and excess fuel then become a problem - for things like fouled plugs.

Lean the engine on the ground until just before it stops. If you then add throttle to taxi and the engine bogs, you are just lean enough. Add a little mixture if you need to taxi faster.

The engine power is so low you cannot lean it too much.

Carl

Yes, I agree with this. The "50 RPM rise" idle mixture setting is where the engine will accelerate smoothly when advancing the throttle for takeoff or go-around. However, this is more fuel than the engine needs to idle at a continuous RPM, hence the reason many recommend leaning for ground ops.

Skylor
 
If the sound of the ticking ( clicking and pinging) correlates with the elevated temperature of one cylinder, my suspicion would be differential expansion of the exhuast pipes . Perhaps a slip joint is too tight or a hanger bracket is binding.

Kinda like old cars and trucks of the 70's cut them off when they were really hot you could hear them ticking , pinging, and clicking for quite a while as they cooled down.

Thanks for the idea, something to check on the next visit under the cowl.

At this point I'm wondering if it is just natural roughness from #3 going lean. I'll pay more attention next time. I wish I could get a video of it but I really don't think a camera in any fashion would pick it up, it's pretty subtle.
 
I have a hard time believing your idle mixture is so perfect that your engine wouldn't benefit from leaning on the ground. If your always preheating your engine to 200ish degrees and thats the temp you adjusted the idle mixture at I could maybe find some truth in it but that seems like a strech.

Every engine needs a touch more gas to run smooth when there cold. Id really like you to lean the mixture when your idling the engine the next time your getting ready for a flight and see if you get an EGT rise.

It's best to have some leeway adjusted into the mixture for changes in ambient temps and elevations.

I can tell you on my IO-360 I have the idle mixture down to less than a 10RPM rise approaching cutoff But, If I idle at 900RPM during a warmup and lean it out I can raise my EGT's from 1000 to 1200.

My carbed 0-320 in the cherokee was the same also.

I wasn't implying that my mixture is Perfect. Only that it is properly set and I see no ill effects from not leaning further with the red knob. Could I possible make it better with the red knob, sure. Does it provide a meaningful benefit in my case, no. I personally don't care to raise my EGT by 10* via the red knob, as I don't believe there is a meaningful benefit to doing so. If I were fouling plugs or getting deposits in my cylinders, I would certainly feel differently.

I will not go into the details, but believe that running between 750-1200 RPM requires no additional leaning beyond a properly set idle mixture. I was just sharing a contrarian opinion with some anecdotal data. I am not knocking anyone who choses to lean with the red knob and did not intend to start an conflict, just wanted folks to see opinions on both sides of the debate, as some say it is absolutely required.

Where my idle mixture is set, I get a very good acceleration with no bog or hesitation.

Larry
 
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I will not go into the details, but believe that running between 750-1200 RPM requires no additional leaning beyond a properly set idle mixture.
Larry

By "properly set" doesn't that depend on where you set your idle mixture, geographically, elevation and ambient temperature?. You are probably right with your no need for leaning in the taxi when at your home field where the idle mixture was adjusted. If your home field is at low altitude and then you travel to high DA airport now the idle mixture can move from the adjustments made at home. Which doesn't mean a whole lot as the aircraft isn't operated at idle for very long. But there may well be an improvement in leaning during taxi at the new airport DA, unless you were to re-adjust your idle mixture setting while visiting the area, which is unlikely. At our high DAs it is more common to get plug loading on the taxi despite having the idle mixture set on the same field. Burning out the plugs on run-up is a common occurrence if the engine isn't leaned for the taxi to the runway prior to run-up.
 
Second this opinion

I wasn't implying that my mixture is Perfect. Only that it is properly set and I see no ill effects from not leaning further with the red knob. Could I possible make it better with the red knob, sure. Does it provide a meaningful benefit in my case, no. I personally don't care to raise my EGT by 10* via the red knob, as I don't believe there is a meaningful benefit to doing so. If I were fouling plugs or getting deposits in my cylinders, I would certainly feel differently.

I will not go into the details, but believe that running between 750-1200 RPM requires no additional leaning beyond a properly set idle mixture. I was just sharing a contrarian opinion with some anecdotal data. I am not knocking anyone who choses to lean with the red knob and did not intend to start an conflict, just wanted folks to see opinions on both sides of the debate, as some say it is absolutely required.

Where my idle mixture is set, I get a very good acceleration with no bog or hesitation.

Larry

I have to agree with Larry on this one. I was always of the mind that I needed to lean out whenever doing ground operations but after extensive conversations with Don at AFP, my Bendix Servo idle mixture has been set correctly for **my sea-level** home field. I never foul plugs on the ground at my home field. Going to Denver or Big Bear its a different story and lean is the name of the game. This all began because I couldn't get a proper idle mixture setting to stick. I would think I had it dialed in and then it would go rich a couple weeks later. It wasn't obvious but I could tell that something was changing in the idle mixture ever so slightly to cause my idle mixture to enrichen. Sent to AFP and Don let me know I had a leaking bellow between the air/fuel chambers. So I basically had a fuel injected/carburetor like fuel distribution system. Outside the idle circuit, I couldn't detect any symptoms. So my suggestion per Bendix and Don (AFP), you shouldn't need to lean in the idle circuit if set up properly ****AT SEA LEVEL****. Bottom line- the idle circuit leaning was masking the real problem of a compromised air/fuel chamber in the Bendix RSA fuel servo. It's been running great on idle circuit since Don fixed it. Can I lean? Sure and I do at other airports w/higher altitudes and sometimes just out of habit but not needed. My idle is set to 700 rpm with 30-40rpm rise, just checked spark plugs after 50hrs and no balls of lead. I'm a happy camper...
 
Yes, leaning becomes necessas you go up in altitude and presumed that most here know that . If they don’t, i feel sorry for them as it can create serious issues at high DA’s if folks don’t lean from full rich. Though the serious problems are on the TO roll. When i go to dnver, i have no issues at idle eve though i am now rich. Though i am confident that I would have a serious stumble if i just shoved the throttle in without proactive leaning.

I get that this approach doesn’t work for everyone. If I lived in denver, I would probably have my mixture on the fat side to allow trouble free ops at SL. In that case, manual leaning is probably necessary.

By "properly set" doesn't that depend on where you set your idle mixture, geographically, elevation and ambient temperature?. You are probably right with your no need for leaning in the taxi when at your home field where the idle mixture was adjusted. If your home field is at low altitude and then you travel to high DA airport now the idle mixture can move from the adjustments made at home. Which doesn't mean a whole lot as the aircraft isn't operated at idle for very long. But there may well be an improvement in leaning during taxi at the new airport DA, unless you were to re-adjust your idle mixture setting while visiting the area, which is unlikely. At our high DAs it is more common to get plug loading on the taxi despite having the idle mixture set on the same field. Burning out the plugs on run-up is a common occurrence if the engine isn't leaned for the taxi to the runway prior to run-up.
 
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At 800 to 1000 rpm on the ground yiur running at probably8-12 percent power

I lean to the point, on an injected IO360, where the engine starts to run rough then slightly enriched it.

Your cylinder temps should not barely be in the yellow in the low end range and egts are not really a factor

Enriched for the run up, lean for elevation with run up power or slightly more rich for takeoff if at higher elevations.

It’s what I have used over my history.

Jack
 
At 800 to 1000 rpm on the ground yiur running at probably8-12 percent power

I lean to the point, on an injected IO360, where the engine starts to run rough then slightly enriched it.

Your cylinder temps should not barely be in the yellow in the low end range and egts are not really a factor

Enriched for the run up, lean for elevation with run up power or slightly more rich for takeoff if at higher elevations.

It’s what I have used over my history.

Jack
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