Mixture too rich?

[bavareze]

Hi there!

 

suppose you look at a '63 mooney m20c and see some black dirt on the right nose wheel door, obviously from exhaust fumes.

 

you wash it, can't really clean it all because the paint got stained

 

then after flying another 10hrs you wipe it and you see that much new deposit on the door. (obviously the deposit happens only with the door open, so think about 5 engine starts and 10 taxi/runup and maybe 20 takeoffs)

 

would you believe something is wrong?  Like mixture too rich? or is it normal to see that deposit there?

 

the JPI shows around 1200F average while opening the throttle for runup with mixture full rich (sea level) and then during cruise 1450-1500 while leaned.

 

Could it need be leaned more during taxi?

 

Thanks!

[Hank]

That's much more than I have on my C, ever. 

On the ground, I lean enough that I need to richen the mixture to taxi uphill. Runup aand takeoff are Full Rich. What is your oil consumption like?

[Guest]

When you pull the mixture to shut the engine off how much rise to you get before the engine quits?

Anything over 25 RPM is too rich, then as Hank points out you can lean further manually for ground operations.

Clarecne

[Shiny moose]

The inside of that tailpipe should not be black, but a lighter tan/gray. Check your mixture setting as M20Doc stated. 

[jlunseth]

You should lean to the peak of idle rise.  When you are at idle and lean the mixture, the RPM’s will increase anywhere from 25-75 RPMs.  That’s idle rise.  Lean to the peak of it, the most idle rise you can get, and leave it there.  Actually, in my aircraft I find I need to be a little richer than peak idle rise to be able to accelerate at all for taxi (such as to move the plane from a dead stop).  There are actually three times your gear doors are exposed to the exhaust, and the one you have not mentioned is approach.  During approach we all cut the power back (as we are supposed to), and many pilots put the mixture in to be “ready for a go around.”  My aircraft engine operation is completely different from yours, mine is an injected turbocharged 231.  But I can tell you that if you do that - make the mixture rich at low power - the engine will burble from running too rich.  So I don’t, I lean it out during the approach and if a go around is needed, I enrich the mixture first and foremost.  However, I am guessing your mixture is set too rich, it should probably be looked at.  

[carusoam]

+1 for the opinion of that's not right....

+1 for testing mixture with the rpm rise on the way to mixture cut off...

At least my C didn't do that.

Best regards,

-a-

[Skates97]

I have a light gray spot there on my door, almost blends in with the off-white color of the plane.

[milotron]

My M20K looks like that too, as did another 20K net to me. I lean it way out on the ground also. I think it is from take-off as the aiming of the exhaust pipe should aim the air flow away from the door during ground ops. Airflow during take off or descent would push it back to the gear doors.

I just wipe it off. Being a turbo, not much I can do about the take off rich condition ( my fuel flow if at the book settings ); I lean it out during descent like @jlunseth does for the same reasons.

 

iain

[jlunseth]

Just now, milotron said:

My M20K looks like that too, as did another 20K net to me. I lean it way out on the ground also. I think it is from take-off as the aiming of the exhaust pipe should aim the air flow away from the door during ground ops. Airflow during take off or descent would push it back to the gear doors.

I just wipe it off. Being a turbo, not much I can do about the take off rich condition ( my fuel flow if at the book settings ); I lean it out during descent like @jlunseth does for the same reasons.

 

iain

I agree.  The only thing I would say is that when the engine is properly leaned in all phases of flight, the residue on the gear doors is lighter and brown in color, not that dark black in the OP’s photo.  That looks too rich to me.

[milotron]

14 minutes ago, jlunseth said:

I agree.  The only thing I would say is that when the engine is properly leaned in all phases of flight, the residue on the gear doors is lighter and brown in color, not that dark black in the OP’s photo.  That looks too rich to me.

That I agree with. Mine is clearly brown, not as dark as that.

[bavareze]

ok so next time I'll go I'll do the idle rise test and post results.

then probably I should try to do approach and landing a little lean and see what I get.

 

[pinerunner]

I agree with the advice to lean aggressively for taxi but takeoff is the one place you want it the richest. I remember an article by Deakins where he reccommended you fight with your A&P and get him to set the mixture even richer then he normally would for takeoff, to get maximum protection from detonation. Once good airflow established then start leaning. Trouble with his recommendations is they get kind of complicated so I don't do all of them and stick with a simplified version.  If I need a secretary to read the instructions to me then I'll take the easier road. My nose wheel door got less stained after I started leaning for taxi but it still gets dirty.

I'd check my spark plugs and if they look fine I wouldn't worry too much about being too rich. Do you have an engine monitor and a fuel flow indicator? 

[Hector]

1300 hours in my 67 C and my doors are not stained. Lots of good leaning advice, but I still would want to know what your oil consumption is.


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[bavareze]

ok here's the deal my friends:

 

the rpm gauge is nice and tight when over 1200rpm but gets shaky when close to idle so I can't really tell the if I can get the "lean idle rise"

I have a JPI engine analizer for temperatures but without fuel flow.

oil usage is I guess around 1qt for 5hrs but lately I have been doing only practice flights with many high power settings such as chandelles and takeoffs, no actual cruise time.  I replaced all 4 cylinders and pistons some 150hrs ago with rebuilt ones.  

what's an ok oil consumption?

 

[carusoam]

Normal oil usage in an O360.... is around one qt every 9 or 10 hours...

High power and high attitude tends to use up or send oil overboard out the vent...

Based on aging memory of my M20C...

Best regards,

-a-

 

[Hank]

Anthony is about right on oil usage. It generally takes me 12-15 hours after an oil change before I need to add any, then each quart comes a little quicker. My engine just passed 800 hours.

It's important to follow proper break in procedures with new cylinders. If you're adding oil every 5 hours, I'd talk to the mechanic who did your cylinders and see if he has any advice; at 150 hours, though, you're probably beyind any type of warranty.

[bavareze]

well to me it looks like a lot of unburned oil might be coming out as vapor through the breather pipe.  I remember seeing an advertisement for an air-oil separator that could be installed on these engines to save the oil.  do you guys use one of those?  maybe that's the case and cylinders are ok.

 

also, I think the oil consumption is much lower when I have 5.5qt in.  but when I put 7 then it goes quicker.  So that reinforces my idea that the oil is being blown out rather than burned.

Edited January 17, 2018 by bavareze
need to add something

[Hank]

I put in 7 qts only when changing oil/filter. Then I never refill above 6 qts, or it gets blown out. Your belly will tell the tale.

[Shadrach]

2 hours ago, Hank said:

I put in 7 qts only when changing oil/filter. Then I never refill above 6 qts, or it gets blown out. Your belly will tell the tale.

^^^^this!

In my experience, short hops and pattern work will use more oil than steady state cruise operations. Oil temp if also a factor in usage.

Also, with a carbureted engine, leaning to rough and enrichening to just smooth for ground ops (or air ops for that matter) is the easiest and safest way to make good mixture choices. 

 

[Hank]

21 minutes ago, Shadrach said:

Also, with a carbureted engine, leaning to rough and enrichening to just smooth for ground ops (or air ops for that matter) is the easiest and safest way to make good mixture choices. 

 

My engine is smooth at any leaning on the ground, until it gets so lean that it won't run. I pull it back ~2/3 to Idle / Cutoff; when I can't taxi uphill, I know it's right. I have limited experience with injected engines (10-12 hours in an F, and 4-5 in an A36), but it seems like my C is quicker and easier to lean in the air. Maybe it's the EGT probes, I dunno. 

[jaylw314]

On 1/17/2018 at 12:56 AM, bavareze said:

ok here's the deal my friends:

 

the rpm gauge is nice and tight when over 1200rpm but gets shaky when close to idle so I can't really tell the if I can get the "lean idle rise"

I have a JPI engine analizer for temperatures but without fuel flow.

oil usage is I guess around 1qt for 5hrs but lately I have been doing only practice flights with many high power settings such as chandelles and takeoffs, no actual cruise time.  I replaced all 4 cylinders and pistons some 150hrs ago with rebuilt ones.  

what's an ok oil consumption?

 

That might explain why your idle mixture might not be set correctly--your mechanic may not be able to do it if the rpm gauge wobbles too much at idle!

[bavareze]

On 1/20/2018 at 1:07 PM, jaylw314 said:

That might explain why your idle mixture might not be set correctly--your mechanic may not be able to do it if the rpm gauge wobbles too much at idle!

Is idle mixture supposed to be adjusted during the annuals or is with carburetor installation?  I did already a few annuals but nobody did that adjustment.  I guess there won't be a problem picking up the impulse from the coil to tell accurate RPM even without a mechanical RPM gauge, if needed

 

Anyways, the other day I flew to Grand Canyon.  Left with 6 quarts oil, after a 4.5hrs round trip the oil was down to 5.8 quarts, so way less than 1 quart per 10hrs during this kind of flight.  I will measure again when I have a chance.  

 

 

[carusoam]

A few things come to mind...

1) A difference of 2/10ths is a challenge to measure accurately... Depending how much oil stays up in the engine and oil cooler or descends into the oil sump...

2) Oil doesn't seam to burn or dissapear very evenly on a flight...

3)  a long flight at 12k’ seems to burn a lot less than one flight of T/O and landing practices... high power and high angle of attack have a tendency to use or blow oil overboard.  Low power cruise at 12k’ doesn’t push oil toward the case vent, or push it past the oil rings...

PP thoughts only not a mechanic...

Best regards,

-a-

[jaylw314]

20 hours ago, bavareze said:

Is idle mixture supposed to be adjusted during the annuals or is with carburetor installation?  I did already a few annuals but nobody did that adjustment.  I guess there won't be a problem picking up the impulse from the coil to tell accurate RPM even without a mechanical RPM gauge, if needed

I don't recall it being a required part of annual/100 hour inspections.  It would only be addressed if the IA noticed it, if it was grossly bad, or if you brought it up as a squawk or related issue

[Cyril Gibb]

8 hours ago, jaylw314 said:

I don't recall it being a required part of annual/100 hour inspections.  It would only be addressed if the IA noticed it, if it was grossly bad, or if you brought it up as a squawk or related issue

I can't see an annual inspection not doing a complete runup including mags/mixture/etc.  Gladys just came out of this years annual.  At Clarences shop a pre and post annual runup is done.  It's also included in the Mooney Annual/100 hour inspection guide: http://67m20e.com/Mooney 100 Hour Annual.pdf