Mixture Rich or Best for ground ops

[Mooney-Shiner]

Ever since my first post in this great community, one of the first things said to me was to lean the engine ruthlessly on the ground.  It made all kinds of sense since I have fouled my spark plugs quite few times before. Still it was a deviation from the original 1967 POH that directs to keep the mixture “full rich” for ground ops for engine cooling.  It also directs to have mixture full rich in addition to boost pump on for RUNUP checks.

On the runup the other day, I went mixture full rich with the boost pump on (as per original POH)  and instantly flooded the right bottom plugs and caused significant RPM drop during the right mag only check. I pulled the bottom two plugs and witnessed them soaked with fuel. I cleaned, dried and re-installed them. As an experiment for the next runup, the mixture was full rich but left the boost pump off. The engine was performing great with both mags firing within specified parameters. Of course, for take off I used the mixture full rich with the boost pump on and had no issues.

I know there are different schools of thought on the mixture leaning ritual in this great community.  So I would like to see what should be an optimal mixture/boost pump settings for the runup for IO360 equipped Pre-Js?

Thank you, crew!

Edited November 24, 2021 by ukrsindicat@yahoo.com

[1964-M20E]

I do lean aggressively on the ground after startup and have not had fouled plugs.  I watch the RPM and look for a slight decrease in RPM.  When doing my run up I increase the mixture but do not go full rich.  After the run up I lean it back out again.  Generally I have to add mixture when I go to taxi this also helps you not to forget to go full rich for takeoff.  I use the boost pump for starting and takeoff.

 

 

[MikeOH]

I ground lean very aggressively.  To taxi I need to advance the mixture, not the throttle.  For run-up I do NOT go to full rich, either.  I can't remember the last time I've had a fouled plug. Boost for start, take-off, and landing.

[201er]

I’m LOP for pretty much everything but the takeoff/climb including ground operations. I lean for peak RPM on runup which is probably just a little rich of peak. Prevents fouling and tests things out well. 
 

Have no fear taxiing LOP, they say you can hurt the engine no matter how you lean it when below 60% power.

[201er]

Oh another thing I learned is to taxi with the mixture as far back as possible without quitting. This way if you forget to push it back in for takeoff, you’ll stumble the engine when you advance the throttle rather than cause detonation.

[DCarlton]

13 minutes ago, 201er said:

Oh another thing I learned is to taxi with the mixture as far back as possible without quitting. This way if you forget to push it back in for takeoff, you’ll stumble the engine when you advance the throttle rather than cause detonation.

I've done that by accident but never as SOP.  :>   Sounds like I need to work on my leaning procedures and lean more aggressively on the ground.  

[ilovecornfields]

With an engine monitor I think you actually get better information doing a run up with a lean mixture than with a rich one -  just don’t freak out when the RPM drop is higher than expected. 

[DCarlton]

13 minutes ago, ilovecornfields said:

With an engine monitor I think you actually get better information doing a run up with a lean mixture than with a rich one -  just don’t freak out when the RPM drop is higher than expected. 

So you use the engine monitor to find LOP at run up RPMs, then do the mag check and look for the uniform EGT increase?  I typically operate 300 feet above sea level and don't do much leaning on the ground.  I need to improve my SOP.

Edited November 24, 2021 by DCarlton

[Mooney-Shiner]

Thanks, guys. Great knowledge


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[Marc_B]

https://www.advancedpilot.com/articles.php?action=article&articleid=1844
 

came across this last night looking at APS. As @201er mentioned, Deakin suggests leaning enough that it would stumble if you forgot to enrichen on takeoff roll.

[ilovecornfields]

8 hours ago, DCarlton said:

So you use the engine monitor to find LOP at run up RPMs, then do the mag check and look for the uniform EGT increase?  I typically operate 300 feet above sea level and don't do much leaning on the ground.  I need to improve my SOP.

That seems like a lot of work! When it’s time to do the run up (I wait until the CHTs are above 250 and oil temp above 100) I leave if leaned, go to 1600 RPM cycle the prop and hit “normalize.” Then I make sure the EGTs rise on all 6 cylinders when on a single mag then go back on both mags. The RPM drop will be higher but the engine still runs smoothly. I don’t even know if I’m ROP or LOP, I’m just a lot leaner than full rich. 
1600 RPM seems to eat less rocks than 2000 RPM. My prop thanks me for that.

[N201MKTurbo]

29 minutes ago, Marc_B said:

https://www.advancedpilot.com/articles.php?action=article&articleid=1844
 

came across this last night looking at APS. As @201er mentioned, Deakin suggests leaning enough that it would stumble if you forgot to enrichen on takeoff roll.

This is extremely important advice! Once about 20 years ago, I forgot to richen the mixture on takeoff. 

4 pistons and rings is about $1000, don't do it!

That was the price of parts, I was doing the grunt labor. If you were paying someone to fix it you can double the price.

Edited November 24, 2021 by N201MKTurbo

[PeteMc]

27 minutes ago, ilovecornfields said:

1600 RPM seems to eat less rocks than 2000 RPM

I was also taught to pull the power back to around 1600 for the prop/gov check.  But checking the plugs and mag system I've always been told by mechanics to do it at the higher 2000 RPM (or at least 1800+).

 

[EricJ]

The POH on my J essentially says to do the runup with mixture full rich, but has a note saying that if there is doubt about the ignition system that you can retest at a leaner mixture.   Once in a while if I get a slightly excessive mag drop it'll go away if leaned to peak rpm. 

Otherwise on the ground I have it pulled way back toward idle cutoff.    One of the (many) advantages of having a quadrant is that it's pretty easy to see how far it is from the end of travel.

 

[kortopates]

I was also taught to pull the power back to around 1600 for the prop/gov check.  But checking the plugs and mag system I've always been told by mechanics to do it at the higher 2000 RPM (or at least 1800+).
 

no need for 2000; especially with an engine monitor since you can see each plug fire independently- that’s the best information you can get from a run up!


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[lotsofgadgets]

Lycoming has published a service instruction aimed at training aircraft, however our IO-360's will benefit from following the process as well.  Basically lean for best power on the ground (RPM just drops) 

 

The flight training environment makes an engine more susceptible to spark plug fouling, decreased efficiency, and excessive fuel consumption. Some of the flight training profiles that cause these conditions include over-priming, prolonged idling, a taxi at low engine speeds, and extended operation at full rich mixture. This Service Instruction identifies recommended procedures that can decrease the aforementioned effects on the engine.

 

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

[Ragsf15e]

Everyone above nailed it, but to your second point, I lean aggressively like everyone above and have never had my engine heat up much on the ground.  In the air if you go lop it’s actually cooler.  On the ground very lean seems plenty cool.  I suppose if you were waiting a long time for takeoff on a very hot day, you might keep an eye on it, but temp doesn’t seem an issue with very lean ground ops.  Your plugs will thank you!

[Shadrach]

13 hours ago, DCarlton said:

So you use the engine monitor to find LOP at run up RPMs, then do the mag check and look for the uniform EGT increase?  I typically operate 300 feet above sea level and don't do much leaning on the ground.  I need to improve my SOP.

Just pull the mixture until the engine is just rich of rough.  That is the most taxing test of the ignition system. There is no need to set run-up power with EGT.  Incidentally, a properly set up Lyc IO360 typically does not typically foul plugs even when ground run with the mixture full rich.

Edited November 24, 2021 by Shadrach

[jaylw314]

17 hours ago, ukrsindicat@yahoo.com said:

On the runup the other day, I went mixture full rich with the boost pump on (as per original POH)  and instantly flooded the right bottom plugs and caused significant RPM drop during the right mag only check. I pulled the bottom two plugs and witnessed them soaked with fuel. I cleaned, dried and re-installed them. As an experiment for the next runup, the mixture was full rich but left the boost pump off. The engine was performing great with both mags firing within specified parameters. Of course, for take off I used the mixture full rich with the boost pump on and had no issues.

Wait, what?  Does the POH actually say do the runup with the boost pump on??  That doesn't make sense, that will mask a problem with the engine-mounted fuel pump.  That's the one you want to test on the runup, you've already tested the electric fuel pump during startup...  My J POH does not specify to turn the electric pump on during the runup, and it's the same motor.

On top of that, you should NOT be able to flood the motor under any normal settings.  If mixture full rich floods the engine at any throttle setting, you have some kind of serious problem, like mixture set WAY too rich.

Edit: Okay, maybe if you're taking off at super high DA you could flood the engine, but this time of year I'm guessing not  I'm guessing you're in Ukraine?

Edited November 24, 2021 by jaylw314

[DCarlton]

3 hours ago, lotsofgadgets said:

Lycoming has published a service instruction aimed at training aircraft, however our IO-360's will benefit from following the process as well.  Basically lean for best power on the ground (RPM just drops) 

 

The flight training environment makes an engine more susceptible to spark plug fouling, decreased efficiency, and excessive fuel consumption. Some of the flight training profiles that cause these conditions include over-priming, prolonged idling, a taxi at low engine speeds, and extended operation at full rich mixture. This Service Instruction identifies recommended procedures that can decrease the aforementioned effects on the engine.

 

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

I printed this for reference and noticed a few things I can improve on.   Letting the engine warm up at 1200 (which is higher than I usually do), and lean and let the engine stabilize before shutdown (which is something I usually rush).  Thanks.  

[Mooney-Shiner]

1 hour ago, jaylw314 said:

Wait, what?  Does the POH actually say do the runup with the boost pump on??  That doesn't make sense, that will mask a problem with the engine-mounted fuel pump.  That's the one you want to test on the runup, you've already tested the electric fuel pump during startup...  My J POH does not specify to turn the electric pump on during the runup, and it's the same motor.

On top of that, you should NOT be able to flood the motor under any normal settings.  If mixture full rich floods the engine at any throttle setting, you have some kind of serious problem, like mixture set WAY too rich.

Edit: Okay, maybe if you're taking off at super high DA you could flood the engine, but this time of year I'm guessing not  I'm guessing you're in Ukraine?

I know...Tough to believe but the original 1967 POH actually says that.  I'm in the good, ol' home of the brave.

I had something similar happening today again but without boost pump. I guess I should have leaned even more aggressively on the taxi and run-up with a mixture right above roughness as knowledgable folks suggest above. 

Thank you  for such awesome recommendations, guys.

[jaylw314]

Wow, that's so odd.  Anyone know why they did that?

I thought you were in Ukraine because your handle looks like it starts with some of the airport identifiers I see in Digital Combat Simulator   I've been playing that a bit too much lately...

Edited November 24, 2021 by jaylw314

[N201MKTurbo]

20 minutes ago, jaylw314 said:

Wow, that's so odd.  Anyone know why they did that?

It is a takeoff checklist. It is getting you ready for takeoff. you are verifying that the engine works in the takeoff configuration.

[jaylw314]

15 minutes ago, N201MKTurbo said:

It is a takeoff checklist. It is getting you ready for takeoff. you are verifying that the engine works in the takeoff configuration.

That would make sense if the boost pump was off somewhere during the runup, right?  After all, the takeoff checklist does include turning off the boost pump at some point.  On takeoff, I'd much rather find out the engine runs with the boost pump off but not on, than finding out it runs with the boost bump on but not off.  The former I'll find out immediately and can abort.  The latter I will find out at a fairly inopportune time...

[A64Pilot]

20 hours ago, 201er said:

I’m LOP for pretty much everything but the takeoff/climb including ground operations. I lean for peak RPM on runup which is probably just a little rich of peak. Prevents fouling and tests things out well. 
 

Have no fear taxiing LOP, they say you can hurt the engine no matter how you lean it when below 60% power.

I have not read the whole thread,but this is the most important statement that can be in this thread, if you lean, lean it so lean that you can’t attempt a take-off, or one day if you don’t, you will and it could work out bad, you can’t hurt it at low power

Before I moved here, they lost two very experienced as in over 10,000 hour aviators in a Bonanza that took off leaned out and I guess didn’t discover their mistake.

I assume they got to talking to each other and missed going full rich, but that’s a guess.

Edited November 25, 2021 by A64Pilot