how to lean the mixture if..?

[kommers]

my 1962 M20C has no temp indicator for it?

 

I typically just pull the red knob one inch out, but I am sure this is not the best setting, and this probably needs to be adjusted with altitude. Any advice?

 

 

thank you

[midlifeflyer]

Go back to student pilot 101 when you leaned the mixture on a 152 on your verity first dual cross country: Lean to engine roughness then enrichen to engine smoothness (it actually does an excellent ballpark even with an EGT and fuel flow meter)

[EDNR-Cruiser]

+1 for midlifeflyer  - That is the way to go with ANY piston-engine...

[Hector]

Lean to roughness then enrich should work just fine.  As an added measure of security for a cruise setting choose a combination of RPM + MP that adds up to 46 which is the target range for an M20C for 65% power (i.e 2400 RPM and 22" MP).  This way, you will not hurt anything regardless of your settings.

[ryoder]

When you start it, after checking oil pressure, immediately lean like crazy until it almost shuts off and then push back in a quarter inch. No need to run rich on idle fouling the plugs. In the C you need to lean aggressively as long as the CHT is cool enough to not require the extra gas to cool it off. I don't go full rich till short final or when using takeoff power at sea level,

[ryoder]

FYI I am one of the most junior members here but I struggled with fouling until I really took control of the mixture.

[DXB]

FYI I am one of the most junior members here but I struggled with fouling until I really took control of the mixture.

I am more junior than you and am also now struggling with fouling.   I've been leaning for taxi some, but have fouled multiple times. Based on EGT, it's always cylinder #2.    I've been able to clear it in the past.  Yesterday I got a left mag drop >200, and I couldn't clear it after several increasingly aggressive attempts. This is particularly frustrating as I have Champion fine wires on the bottom, which supposedly don't foul easily.  Luckily a mechanic was around on the field in the late afternoon on a Saturday and took pity on me.  He cleaned the bottom plugs, and this fixed it. Today I leaned like crazy.   Also when he pulled the plugs, there was oil on #2- I think you had something like this once?.  Notably, EGT and CHT on #2 have always run the hottest (by a lot) for reasons unclear to me or multiple A/Ps I've asked.  

[ryoder]

I have tempest fine wires and they work great but one lower plug did oil foul. You might alter your ground operations a bit to help burn off the oil. Maybe run a slightly higher rpm like 1100 and keep the cowl flaps closed until the cylinders get warm enough.

My oily plug hasn't oiled up yet so I think I got lucky. Do you fly with too much oil? I could be wrong but I think if you have too much oil and weak oil control rings they tend to foul more. My mechanic out in 7 quarts after the oil change and I oil fouled not long after that. Could be a coincidence.

[midlifeflyer]

I am more junior than you and am also now struggling with fouling.   I've been leaning for taxi some, but have fouled multiple times.   

 

I flew multiple types in Colorado - where leaning in the ground isn't just a nice thing to do, it's a necessity -  for 20 years. The only airplane that I ever had to return to the ramp because I couldn't clear fouled plugs was an M20C. Only happened once. Lean aggressively; power needed on the ground is so little, there's no reason not to.

[DXB]

I have tempest fine wires and they work great but one lower plug did oil foul. You might alter your ground operations a bit to help burn off the oil. Maybe run a slightly higher rpm like 1100 and keep the cowl flaps closed until the cylinders get warm enough.

My oily plug hasn't oiled up yet so I think I got lucky. Do you fly with too much oil? I could be wrong but I think if you have too much oil and weak oil control rings they tend to foul more. My mechanic out in 7 quarts after the oil change and I oil fouled not long after that. Could be a coincidence.

Could be- my mechanic filled all the way to 8 quarts for some unknown reason at first oil change after IRAN of cyl #1 (burnt exhaust valve discovered at prebuy). It blew off quickly as expected and then has consumed 1 quart in 16 hrs since then- I only top off to 7.   Still my compression is >70 on cylinder #2 (the one with oiled plug), so I doubt it's leaking past the piston ring.  I worry it's coming through a bad valve guide, and I'm going to end up with another burnt valve in short order.  I guess I'll check the plug again in several hours and dig deeper if it oils again or keeps fouling repeatedly.  Why that front cylinder runs hotter is also a total mystery to me- if it's the leanest one, you'd think it would foul the least, not the most.   

 

I'm trying to taxi at 1100 again.  My transition instructor had admonished me not to ride the brakes so much and drop the power instead.  I'm not sure there is a middle ground here - it's hard to stay off the brakes at 1100, and my field has perpendicular 5k and 7k ft. runways, so there's often a long way to taxi.  

[carusoam]

Taxiing at 1100 rpm, don't you risk departing the runway in the vertical direction?

I think I might achieve 65 KIAS after a few thousand feet.

It is OK to change throttle settings while taxiing....

Too low can cause...

- oil distribution problems.

- charging problems.

Too fast can cause...

- brake wear

- damage by hitting bumps on uneven pavement.

Some ideas to consider,

-a-

[Shadrach]

+1 for midlifeflyer  - That is the way to go with ANY piston-engine...

 

 

It's true it works, but for injected engines, many folks would be leaving a lot of speed and fuel economy on the table. Not to mention CHTs in the mid 200s and Oil temps in the 150s in the winter time.

[Shadrach]

Could be- my mechanic filled all the way to 8 quarts for some unknown reason at first oil change after IRAN of cyl #1 (burnt exhaust valve discovered at prebuy). It blew off quickly as expected and then has consumed 1 quart in 16 hrs since then- I only top off to 7.   Still my compression is >70 on cylinder #2 (the one with oiled plug), so I doubt it's leaking past the piston ring.  I worry it's coming through a bad valve guide, and I'm going to end up with another burnt valve in short order.  I guess I'll check the plug again in several hours and dig deeper if it oils again or keeps fouling repeatedly.  Why that front cylinder runs hotter is also a total mystery to me- if it's the leanest one, you'd think it would foul the least, not the most.   

 

I'm trying to taxi at 1100 again.  My transition instructor had admonished me not to ride the brakes so much and drop the power instead.  I'm not sure there is a middle ground here - it's hard to stay off the brakes at 1100, and my field has perpendicular 5k and 7k ft. runways, so there's often a long way to taxi.  

 

900RPM ought to be adequate to keep oil on the cam once the oil is warm. Don't ride the brakes just jab them a bit every 100' or so if needed. Many instructors don't know shinola about whats happening internally up front, especially model to model variances.

[Hank]

In my C, after start and carb heat check, I pull the mixture about 2/3 towards cutoff. If you lean it too much, it will stumble when you try to move, just push it towards Rich a little.

[midlifeflyer]

It's true it works, but for injected engines, many folks would be leaving a lot of speed and fuel economy on the table. Not to mention CHTs in the mid 200s and Oil temps in the 150s in the winter time.

Even if that's the case you'll be in the ballpark, typically somewhat rich of peak, and not out in the parking lot. I've compared the "simple" method with the more sophisticated ones in multiple aircraft, even fuel-injected Bonanzas and Mooney Js and the result are surprisingly close. Of course, in any aircraft with EGT, CHT, fuel flow, etc, the ballpark setting should be tweaked. And I do tweak to get to my desired final  targets.

[midlifeflyer]

In my C, after start and carb heat check, I pull the mixture about 2/3 towards cutoff. If you lean it too much, it will stumble when you try to move, just push it towards Rich a little.

Whether 2/3 or 1" or whatever-you-choose works depends on density altitude. And some aircraft are more squirrely in mixture than others. One size definitely does not fit all.

[ryoder]

900RPM ought to be adequate to keep oil on the cam once the oil is warm. Don't ride the brakes just jab them a bit every 100' or so if needed. Many instructors don't know shinola about whats happening internally up front, especially model to model variances.

Yeah the tach is not very accurate so 1100 might be 1050. I dont like going that fast but the engine likes it. Prolonged low idle results in worse mag drops and rougher running. It also has low oil pressure. I hit the brakes a bit to bring the speed down instead of riding them.

[Hank]

Whether 2/3 or 1" or whatever-you-choose works depends on density altitude. And some aircraft are more squirrely in mixture than others. One size definitely does not fit all.

Agreed, it must be modified based on DA. But there's little enough change from Lower Alabama to Philly that our Cs should lean very similarly. Your injected engine, also at a similar elevation, is most likely different. We run 3-5 psi fuel pressure in flight, that won't even prime hours on the ground.

[Shadrach]

Even if that's the case you'll be in the ballpark, typically somewhat rich of peak, and not out in the parking lot. I've compared the "simple" method with the more sophisticated ones in multiple aircraft, even fuel-injected Bonanzas and Mooney Js and the result are surprisingly close. Of course, in any aircraft with EGT, CHT, fuel flow, etc, the ballpark setting should be tweaked. And I do tweak to get to my desired final  targets.

Lean until rough and enrichen until smooth would likely put my richest around 70-80 LOP at any altitude under around 8000 feet. That's a lot of speed left on the table and it's also inefficient. It works great in carbureted engines and won't hurt a thing on an injected engine (it's how my Father in law runs his Super D), but I have my doubts that will leave the majority of injected lycoming 4 bangers "somewhat of rich of peak". I will give it a try and report back.

[ArtVandelay]

Lean until rough and enrichen until smooth would likely put my richest around 70-80 LOP at any altitude under around 8000 feet. That's a lot of speed left on the table and it's also inefficient. It works great in carbureted engines and won't hurt a thing on an injected engine (it's how my Father in law runs his Super D), but I have my doubts that will leave the majority of injected lycoming 4 bangers "somewhat of rich of peak". I will give it a try and report back.

It leaves me around 40-50 LOP, YMMV, but I think if your engine gets rough on the ROP side you have a problem

[DXB]

It leaves me around 40-50 LOP, YMMV, but I think if your engine gets rough on the ROP side you have a problem

Something I don't quite grasp here- On a carb. engine, would one expect this to leave the leanest cylinder LOP but then maybe some cylinders at peak, and some ROP?  Doesn't seem like the healthiest situation.  

[Hank]

I'm beginning to have limited success going LOP with my C since the doghouse has been repaired at the last two annuals,and my carb heat box was rebuilt this annual, too.

I'll try it at altitude this weekend, headed to a wedding, but Sunday around noon I was able to reach almost 25°LOP with only slight roughness at 3000 msl; it used to start if I pulled mixture much past peak even though the EGT needle wouldn't move. Look for updates next week, I'll have two long, high chances to experiment.

[Shadrach]

Something I don't quite grasp here- On a carb. engine, would one expect this to leave the leanest cylinder LOP but then maybe some cylinders at peak, and some ROP? Doesn't seem like the healthiest situation.

You are correct, but at altitude it shouldn't hurt a thing.

[Hank]

Something I don't quite grasp here- On a carb. engine, would one expect this to leave the leanest cylinder LOP but then maybe some cylinders at peak, and some ROP?  Doesn't seem like the healthiest situation.

It doesn't hurt anything at altitude, as it's low power, but that imbalance is why it runs so rough. Richen it until the rough goes away, that's about all you can do without at least a single-point EGT. My plane still has just the one it left the factory with, but someone along the way added the optional Carb Temp gage, a very handy instrument at times.

[ArtVandelay]

You are correct, but at altitude it shouldn't hurt a thing.

On a J, when at 4000' and 2200 RPM, you are at reduced power, but at higher RPMs you are not, you want to be below 65% HP, so after leveling out, set power, RPM as desired, then mixture...