Fouled plug questions.

[Mcstealth]

Couple of questions on fouled plugs. I have been flying a Cherokee 180 since the Darter went down. This plane is flown regularly. Each time I get in and do the run up, the second click runs rough. I then do a lean rpm run to clear the plugs. Repeat the run up procedure to confirm the carbon burned off. 

I lean to taxi, lean after takeoff  and cruise, etc, etc....

When I get back from my XC, I do a run up to see if the fouling returned. The answer is yes. This has happened the last three trips of 1.4 hours each. I don't know how the others fly the plane, but I doubt they lean as consistently as I do. I "feel" as if I lean enough, but what do I know?

What is the best practice for burning off carbon? What is best practice for leaning? Is there something mechanical going on?

Thanks, David. 

[201Steve]

It’s probably oil, not carbon. 
 

if you have engine monitor, you can see which cylinder it is during the mag check. If you don’t have an engine monitor, pull all your bottom plugs and you’ll find one with a film of oil on it. Cylinder/ring problem, most likely. 
 

not a mechanic 

[Hank]

How are you leaning, David? I have the same engine in my C, it's very simple. What altitude and power settings do you cruise with?

Do you lean on the ground for taxi? How far?

Lots of little things you can do, but if it's an oil leak they won't help much. 

[A64Pilot]

Sometimes a plug needs to be physically cleaned, high power and lean can only burn a tiny bit off.

But it depends on what’s fouling the plug, 99% of the time “carbon” is actually oil coked onto the plug, aircraft engines are designed to burn oil, that’s why our oil must be ashless and cars who aren’t designed to burn oil don’t need ashless oil. But even ashless oil cooks down to a carbon like deposit.

So sometimes you have to pull the plugs and clean out the burnt oil that’s caked around the insulator. Eventually you won’t be able to burn it off during run up.

And some engines / cylinders burn more oil than others too.

[Mcstealth]

17 hours ago, Hank said:

How are you leaning, David? I have the same engine in my C, it's very simple. What altitude and power settings do you cruise with?

Do you lean on the ground for taxi? How far?

Lots of little things you can do, but if it's an oil leak they won't help much. 

When I taxi, I pull the lever down half way. The engine does not stumble so maybe I can do more? After takeoff and turning fuel pump off, I pull to lean untill I see the the temp Guage needle move toward the preset redline. How close to the redline do I get? I am sorry I do not know what temp the red line is set at. No engine monitor. 

I am flying 4500-5500ft, 2400rpm. Between 110-120 MPH. 

I go rich at Takeoff and landings with fuel pump on. 

[N201MKTurbo]

Do you richen your mixture on descent? I was taught that when I learned to fly, but I have no idea why anybody would do that. The only reason to richen the mixture is if the engine starts to stumble or you are doing a go around. 

[carusoam]

D,

How many hours on the engine…?

Do you know the oil use rate…? 1qt per 9-10hrs is probably normal….

There are typically two things that have a tendency of interfering with the spark…

1) Lead build-up… where leaning on the ground is good for clearing it…

2) oil soaking… where oil pools on the lower plug… more challenging to burn off as oil usage increases…

 

Of course… a weakened spark is easier to interfere with… it may help to know how many hours are on the mags…

Pulling the lower plugs may identify the worst offender…  be on the look out for lead balls, and oil soaking….

The engine monitor is going to be important when you get your Mooney!   
 

PP thoughts only, not a mechanic…

Best regards,

-a-

[jaylw314]

2 hours ago, Mcstealth said:

When I taxi, I pull the lever down half way. The engine does not stumble so maybe I can do more? After takeoff and turning fuel pump off, I pull to lean untill I see the the temp Guage needle move toward the preset redline. How close to the redline do I get? I am sorry I do not know what temp the red line is set at. No engine monitor. 

I am flying 4500-5500ft, 2400rpm. Between 110-120 MPH. 

I go rich at Takeoff and landings with fuel pump on. 

There's a preset red line on the EGT gauge?  Is there a knob to move it?  I've seen a lot of EGT gauges that have a line you can move around to mark where your peak EGT is, so where it is now may mean nothing unless you do that.  Of course, it it's not moveable, then it DEFINITELY means nothing!

It would be interesting to try leaning until you hear roughness, then richen a tiny bit until it goes away.  Then compare that to where you are leaning before.  If it's still pretty close, then the mixture technique probably isn't the issue.

FWIW during taxi in the carbureted Cherokee 140, I'd typically have the quadrant-style mixture level only about a half inch above cut-off, so it seems typical (well, at least for the PA-28 140 and the M20J IO-360) that you can taxi with barely any mixture travel.

Edited September 22, 2022 by jaylw314

[carusoam]

EGTs with no numbers on them…. Have a movable needle…

One of the lines has an * next to it…

Adjust the needle to match the * when the EGT has peaked…

Alcor probably has the most popular device in aviation….

They have an explanation on how best to use their pseudo calibration technique…

This link gets you a bit closer, but might not have the technique….

https://www.chiefaircraft.com/aircraft/engine-instruments/alcor-gauges-probes/alc-46150.html?gclid=Cj0KCQjwj7CZBhDHARIsAPPWv3dFhnD6aK3SdmyDby7FEoOUFUEXKwffNqwP6AgawG5iv9RUE0WjM7saAoubEALw_wcB

Best regards,

-a-

[Mcstealth]

On 9/23/2022 at 1:43 AM, N201MKTurbo said:

Do you richen your mixture on descent? I was taught that when I learned to fly, but I have no idea why anybody would do that. The only reason to richen the mixture is if the engine starts to stumble or you are doing a go around. 

The checklist says to go rich, so yes though I do agree with you. 

[Mcstealth]

On 9/23/2022 at 2:30 AM, carusoam said:

 

How many hours on the engine…?

1000jrs

Do you know the oil use rate…? 1qt per 9-10hrs is probably normal….

I put in half bottle in six hours. 

 it may help to know how many hours are on the mags…

Owner did not know

 be on the look out for lead balls, and oil soaking….

I will pull them in two weeks when I get back. 

The engine monitor is going to be important when you get your Mooney!   

I'm getting closer. 
 

 

[Mcstealth]

On 9/23/2022 at 3:41 AM, jaylw314 said:

There's a preset red line on the EGT gauge?  Is there a knob to move it?    Yes

It would be interesting to try leaning until you hear roughness, then richen a tiny bit until it goes away.  Then compare that to where you are leaning before.       Okay. I will pay attention and test when roughness shows up.

FWIW during taxi in the carbureted Cherokee 140, I'd typically have the quadrant-style mixture level only about a half inch above cut-off,       okay, pull lever down more. 

 

[PT20J]

First of all, the purpose of ground leaning is to prevent lead fouling by elevating combustion chamber temperatures in the idle/taxi power range to the point where the lead scavenger in the fuel becomes effective. Once a plug is severely lead fouled, it usually won’t clear using the high power/rich mixture burn out technique and must be removed and cleaned.

You only seem to get this fouling on the ground at low power either before or after a flight. Since it clears using the burn out technique, it is likely due to excessive oil in one cylinder. At high power, the condition clears due to increased temperature and perhaps better ring sealing at higher pressure. 

With an engine monitor, it should be easy to figure this out. I would also pull all the plugs and check to see if any are oily. Oil consumption trend, how quickly the oil blackens after an oil change, borescope inspection and compression tests are additional diagnostics. Keep in mind that an oily cylinder with worn rings can show good compression due to the oil sealing the ring cylinder interface.

Skip

[Mcstealth]

5 hours ago, PT20J said:

Keep in mind that an oily cylinder with worn rings can show good compression due to the oil sealing the ring cylinder interface.

Skip

I learned this exact thing on The Darter I am flying. Two cylinders showed low compression,  but I can say I did not feel anything wrong. Power seemed good, no excessive oil consumption that I could tell, no oil down the belly, etc etc.