Leaning: One more time, please.

[N6893U]

Hey Y'all,

I have researched the forums, Lycoming and Mooney manuals, Insight engine monitor manual, and elseware to determine the proper way to lean a carburated O-360 engine on a 1963 M20C. Thought I had it figured out, then read something that made me question myself.

Rather than ask for everyone for their techniques, I thought I would tell you mine, and let you throw stones and recommendations. I should add, I have had the plane for over two years, two annuals with no troubles or issues with the engine, oil or plugs. Here goes.

Taxi in and out--lean aggressively--full rich for run-up

Takeoff--full rich, unless DA>3000 ft

After Takeoff--Gear up--power back to 25/25

Climb-lean to 100oF < peak

Cruise--50oF<peak

Decent--Enrich as required

Land--full rich

CHT always <400

Please give me your opinion, it seems to work OK, but I am always open to suggestion.

Thanks,

Jerry

[carusoam]

It's helpful to have a digital device for all four EGTs/CHTs, Fuel Flow is also helpful for further diagnosis.

My 65C was never able to push LOP. Without the extra instrumentation it is not possible to identify that each cylinder is operating similar to it's neighbors.

The carburetor is not known for delivering even fuel flow and ratios to all four cylinders...

I was able to lean close to peak, but peak was ill defined as vibration and rough running began at that point.

Anyone else have positive LOP experience with a carbureted O360?

Single instrument analog EGT and CHT is a tough way to handle LOP. The risk of over or under leaning one cylinder or another is too great.

As usual run your LOP experiments under low power (high altitude) to avoid unintentional damage...

Are you able to run to a defined peak with your engine and instrumentation, or is it lean until rough, the enrich 50deg?

Best regards,

-a-

[stevesm20b]

I just lean until engine runs rough then enrichen until engine runs smooth.

[carusoam]

Yes Steve,

Using your method and the single EGT gauge you can determine how much ROP your engine actually is...

I way over thought what the OP was asking. Thought he was experimenting with LOP...

My bad...

-a-

[jetdriven]

Remember if you are above 7 or 8K density altitude, there is no mixture setting that can harm your engine as long as CHTs are below 400. You must experiment with your plane to determine what it can deliver. The easiest way to get the maximum economy comes from Walter Atkinson. Lean until you see a 3-5 knot speed loss. Done.

[danb35]

After Takeoff--Gear up--power back to 25/25

Why pull the power back? Do you want to climb slower than necessary? Your engine is certified for continuous operation at full power (and once you're past a few thousand feet elevation, you're not at full power any more anyway). If you have noise concerns, pull the prop back a bit, but there's no need to touch the throttle.

Climb-lean to 100oF < peak

A setting of 100 ROP is a bit lean for the climb, at least for early in the climb. Recommend instead leaning to a target EGT ~= to the sea level EGT at full rich (for me, it's around 1250 degrees).

Cruise--50oF<peak

Setting 50 ROP will yield the hightest CHTs and peak internal cylinder pressures possible. Any mixture setting richer or leaner than this will be kinder to your engine. You'll see best power at 80-100 ROP (and cooler CHTs), and considerably better economy at peak EGT (and, again, cooler CHTs). LOP will give better economy yet, but may not be practical with your engine.

Decent--Enrich as required

Land--full rich

For my engine, "as required" in the descent is not at all. I descend from cruise altitude and land without adjusting the mixture.

CHT always <400

Good, but < 380 is better.

[KSMooniac]

What Dan said...

[Hank]

In my C, I push everything forward for takeoff, and leave it there as I climb unless going above ~7500; then I will lean a little in the climb, watching EGT. If I forget to lean, it will be about 1100º at ~9000 msl, so I'll pull it back a little [target 1200-1250]. "Climb power" is max power, anything less and I won't climb near as well.

If high, I generally run 2500 RPM; if low, 2300; in between, 2400; I use the charts in my Owner's Manual to determine the changeover. Generally 4000-6000/6500 is 2400 RPM. I pull the power back [MP + RPM = 47 or less] accordingly. When nice and high and OK to run WOT, I still pull back enough to make the MP needle move then set 2500 and lean away. My wife can spot "rough" before I notice the needle is peaking, and push it forward a little bit. My goal is to create non-laminar flow in the carb for better atomization and mixing; turbulent flow is even better, but WOT will not do either.

When descending, I establish 500 fpm, trim down, and as MP and EGT increase in the descent I periodically pull them back to whatever my cruise settings were. For step-downs, after leveling off I will reset as above and maintain those values for the next "down" portion.

So far, it's been five very good years.

[N6893U]

Thanks to all you responders, as usual your knowledge is invaluable and much appreciated.

Jerry

[bd32322]

One more thing - you should not reduce rpm at or near full power operations. The reason being, the engine is designed to develop peak pressure from the combustion event once the piston is going away from the cylinder head after reaching top dead center. This way the combustion gives the piston a push. True at least for the engines designed for continuous full power ops.

If you lower RPM at full power, the piston moves towards top dead center slower and if the peak pressure is reached before or close to top dead center, you end up pushing the piston down when its trying to move up. This is not productive towards moving your crankshaft and causes a lot of energy to be absorbed by the cylinder head which shows up as high CHT. Temperature is after all average velocity of the molecules, which in turn is dependent how much energy you have fed those molecules.

If your CHTs are 380 or less, i guess you are fine, but you are probably doing wasted work by not developing peak pressure at the correct time.

If you want to know more, search for a yhread titled "turbo lop" here. I know yours is not turbo, but the thread has a bunch of very interesting articles that explain what I am talking about