Leaning mixture after start-up

[MATTS875]

Hello, quick question.. after start up and all gauges are reading in the green , are you suppose to lean the mixture back?My hanger is a little ways from the runway to do the run up at and did not know if I left the mixture at full rich if it would foul the plugs before run up.Because I am new to this airplane it takes me a little longer going down the checklist.Thanks for any input

[rob]

I lean immediately after start on my M20C, aggressively. I've been told that you can't do any harm doing so, and so far I haven't seen any ill effects. Just be sure to enrich before the runup, or you'll be met with an unhappy stumble when you advance the throttle...

[jetdriven]

Yes, there is no lean mixture setting that can harm it below ~ 65% power.  We lean as much as possible as soon as it is running steady.   Leaning aggressively on the ground, besides keeping your plugs clean, keeps combustion chambers clean and promotes a faster warm up, IE a stoichiometric mixture puts a little more heat into the engine.

[MATTS875]

Perfect. thanks for the reply.  I had not been doing it before and noticed on run up mag drop was a little more than expected.

[Hank]

Quote: MATTS875

Hello, quick question.. after start up and all gauges are reading in the green , are you suppose to lean the mixture back?My hanger is a little ways from the runway to do the run up at and did not know if I left the mixture at full rich if it would foul the plugs before run up.Because I am new to this airplane it takes me a little longer going down the checklist.Thanks for any input

[jetdriven]

If leaned aggressively during runup (or full rich on a high DA day) , yes the mag drop can be a little larger.  Richen slightly and see what that gives you.

Again, you can lean as soon as it is running. Its cleaner, and helps warm up faster.  The oil is what needs to be warmed too.  On a J, there is a white dot on the oil temp guage at 75 degrees F.  POH says not to even do a runup until that oil temp is above the white dot.  I think multigrade oil will warm faster.

Quote: MATTS875

Perfect. thanks for the reply.  I had not been doing it before and noticed on run up mag drop was a little more than expected.

[Shadrach]

I do not believe that ground leaning a Marvel Sheibler carbureted engine will do much if anything. The idle circuit is adjustable by screw and uses vacuum to draw in fuel when the butterfly is closed. The idle float valve is basically either receiving fuel or it is not. If the butterfly is closed, the mixture knob will have little to no effect on fuel metering other than cut-off. Give it a shot and see if you can lean to a maintained 50 RPM rise. I suspect you will not be able to do it as Idle fuel delivery is supplied through a needle that is only adjustable by turning the idle control screw...

[rob]

Quote: Shadrach

I do not believe that ground leaning a Marvel Sheibler carbureted engine will do much if anything. The idle circuit is adjustable by screw and uses vacuum to draw in fuel when the butterfly is closed. The idle float valve is basically either receiving fuel or it is not. If the butterfly is closed, the mixture knob will have little to no effect on fuel metering other than cut-off. Give it a shot and see if you can lean to a maintained 50 RPM rise. I suspect you will not be able to do it as Idle fuel delivery is supplied through a needle that is only adjustable by turning the idle control screw...

[Shadrach]

Quote: rob

 

I'm confused by this statement. I don't think anyone is operating a carbed engine on the ground with the throttle fully out, are they? I don't even know at what speed my engine would idle, but I maintain between 1000-1200 RPM as mentioned earlier in the thread. The mixture control has an effect at these settings, which I can confirm by my fuel flow and engine monitors. So "ground leaning" clearly has an effect on my M20C.

[jlunseth]

I don't know enough about the 20C carb. to disagree at all with Ross's comment that it is (to paraphrase) self-regulating.

There is a phenomenon known as "idle rise" and generally it means that if you idle an engine full rich and then lean it out, the RPM's should increase around 50-75 RPM's, peak, and then fall off again as you continue to lean.  Idle rise is one tool in determining whether an engine's fuel system is properly set up.  What I do in my K, is lean out to about max. idle rise at around 1200 RPM's, and the engine seems happy there.

[rbridges]

Quote: MATTS875

Hello, quick question.. after start up and all gauges are reading in the green , are you suppose to lean the mixture back?My hanger is a little ways from the runway to do the run up at and did not know if I left the mixture at full rich if it would foul the plugs before run up.Because I am new to this airplane it takes me a little longer going down the checklist.Thanks for any input

[Seth]

I always leaned the mixture after start up and during taxi.  In the F Model, it just kept plugs from fouling and also, my F model would "pop" from time to time on the ground - this did not happen as much when I would aggressivlly lean.  I always enrichen for runup, then lean again if not 1st in line.  Unless at high altitude, always go rich at takeoff.

The Missile with the IO-550 I MUST lean or it stumbles and floods at low RPM.  I stumbles and runs rough unless I lean a bit at 1000 RPM, however it runs just fine at takeoff power full rich.  I learned after having the engine stumble and flood on roll out to not actually have full rich on landing, have it about an inch out so that the engine doesn't quit on you on a go around.  It's only happened once, but at altitude, the aircraft stumbled when I had it too rich at a lower power setting - just very finicky with the mixture control. 

So to sum up - yes, I am a fan of and do lean aggresivly on the ground.

-Seth

[Cruiser]

The biggest problem with leaning during taxi is forgetting to go full rich with the mixture before the takeoff roll. You will see some nasty EGT and CHT values and potential engine damage from detonation if the mixture is left too lean for the takeoff.

Always, always, always check throttle, prop and mixture settings before takeoff

[carusoam]

Cruiser,

Good point.  Lean aggressively on the ground.  This way when you push the throttle to go, you get the obvious stumble warning.

If you only lean slightly, high temps on take-off are near guaranteed.

M20C idle should be down around 700 - 800 rpm?  It would be really hard to land if the engine were still pulling 1200 rpm, no?

Best regards,

-a-

[jetdriven]

iPhone won't post replies.  Agreed with Carousam. If you lean it as much as possible to taxi, when you go to take off, the engine will not accelerate above 1500-1700 RPM.  Serves as a reminder.   You are using target EGT method for takeoff and climb, right?

[jlunseth]

What happened to your " before takeoff" checklist?  Use one and you won't ever forget.  Won't forget the cowl flaps either, nor turning your transponder on.

 

[triple8s]

 " You are using target EGT method for takeoff and climb, right?"  JD would you elaborate please?  

[Hank]

I lean my C on the ground at large airports and when waiting in line. Don't rightly know where the engine idles by itself, I keep it at 1000 RPM, which does take some forward movement of the throttle. Landing is, of course, done with the throttle all the way out, but I don't take the time to look at the tach, I'm usually watching the runway.

Target EGT means take off full throttle, full RPM, full rich [just like always] as close to sea level as possible on a day as close to 59ºF as you can get. Observe the EGT, record the number. For all other takeoffs, lean during the climb to maintain that EGT number all the way to cruise altitude. In my plane, that's about 1250-1300ºF. In the summer, I keep it rich longer, with an eye on CHT and Oil Temps. In the winter, extra power and extra lift give extraordinary climb rates. Single-digit preflights are not fun, but the VSI really moves going over the trees!

Yes, the engine does "burble" with the throttle all the way out on short final, and yes, I do push in some throttle to maintain taxi speed and ~1000 RPM after landing. If I'm taxiing several thousand feet, the red lever comes back about halfway [i never notice any change in speed, RPM, sound or EGT, but figure I need to leave it SOME fuel . . . ]. My first trip after getting my PPL, I landed on the second stripe [8000' available], and exited at the first turn--the tower advised me that the FBO was 6000' away. Since then, I've always paid attention to airport diagrams and locating my parking spot; then I adjust the landing to minimize that kind of taxi, since I'm not comfortable taxiing with the ASI pointing to numbers.

[Shadrach]

Quote: triple8s

 " You are using target EGT method for takeoff and climb, right?"  JD would you elaborate please?  

[Shadrach]

Quote: Hank

I lean my C on the ground at large airports and when waiting in line. Don't rightly know where the engine idles by itself, I keep it at 1000 RPM, which does take some forward movement of the throttle. Landing is, of course, done with the throttle all the way out, but I don't take the time to look at the tach, I'm usually watching the runway.

Target EGT means take off full throttle, full RPM, full rich [just like always] as close to sea level as possible on a day as close to 59ºF as you can get. Observe the EGT, record the number. For all other takeoffs, lean during the climb to maintain that EGT number all the way to cruise altitude. In my plane, that's about 1250-1300ºF. In the summer, I keep it rich longer, with an eye on CHT and Oil Temps. In the winter, extra power and extra lift give extraordinary climb rates. Single-digit preflights are not fun, but the VSI really moves going over the trees!

Yes, the engine does "burble" with the throttle all the way out on short final, and yes, I do push in some throttle to maintain taxi speed and ~1000 RPM after landing. If I'm taxiing several thousand feet, the red lever comes back about halfway [i never notice any change in speed, RPM, sound or EGT, but figure I need to leave it SOME fuel . . . ]. My first trip after getting my PPL, I landed on the second stripe [8000' available], and exited at the first turn--the tower advised me that the FBO was 6000' away. Since then, I've always paid attention to airport diagrams and locating my parking spot; then I adjust the landing to minimize that kind of taxi, since I'm not comfortable taxiing with the ASI pointing to numbers.

[Hank]

Yep, jpg's attach well; others not.

Strange how if the idle fuel flow is not controlled by the mixture lever, the more I lean during ground operations at ~1000 RPM the smoother my run-up mag checks are and the less lead buildup my plugs have when I remove them for cleaning. Maybe it's close enough [at least where my idle screws are set] that the mixture lever has some effect at 1000. Runup is always full rich regardless of taxiing usage though.

The first year I had to regularly "clean the mags" at runup due to excessive RPM drop; now that I lean significantly for extended ground ops, I rarely have to do this. [Clarification:  yes, I know it's not the mags, but that's what my CFI always called it. Throttle to 2000; lean for ~50 RPM increase; hold for 60 seconds; full rich; back to 1700, mag check is all better now. Leaning during taxi almost eliminates the need for this. Even though no mixture control of idle fuel flow. YOU explain why it works, I'm just glad that it does.]

[Shadrach]

It works because at 1000RPM you are likely just starting to see the metered jet come on-line and perhaps leaning is keeping the mixture around stoic...or, there is some other factor (new plugs, mags, carb adjustment, etc.).  Next time you're taxing at 1000rpm lean the mixture and see what happens to EGTs. If EGTs rise with each turn of the knob, then you're burning metered fuel. If EGTs remain steady and then briefly rise and the engine quits, then not so much, and your "clean plugs" are the result of some other variable. Do let us know... I have experience with carb'd aircraft, but not much in carb'd Mooneys... I'd like to get the data. Thanks!

[Hank]

Ross--I'll check it over Thanksgiving, that's when I get her back with supposed-to-be non-leaking tanks. But I have a throttle quadrant, with levers to push and pull, rather than knobs that turn. Data will be somewhat compromised. I did replace the cranking capacitor in one mag last winter, other than that no adjustments/repairs/parts exchange since purchase, just less fouling and cleaner plugs the last three years. I'll check the idle RPM too, but from shutdown it seems like it's 700-800 or so--I often push throttle to hit 1000 after stopping in front of the hangar, then lean for a rise of <100 before she shakes and dies.

[jetdriven]

Shock heating your engine to clean the plugs off isn't so good for it either. Leaning during taxi prevents the need for that.  We have only had to do it once in 100 hours, I was checking someone out and he let it idle at 800 rpm a couple minutes.  

[FlyDave]

Quote: jlunseth

What happened to your " before takeoff" checklist?  Use one and you won't ever forget.  Won't forget the cowl flaps either, nor turning your transponder on.