Engine rough before lean of peak

[Camillo]

Hi.
I read some posts but they didn't help me.

When I lean the engine, engine starts running rough before the lean of pick. So I have to enrich it in order to let it run smoother. Approx. I have 770 Celtius degrees EGT on cylinders 2 and 3 and 15° less in cylinders 1 and 4. This happened since ever. Now airplane has 127 hours and spark plugs were moved but not changed (the same that came with the engine). I have a new Lycoming O-320. Airplane is flying since April 2011. Engine is started up regularly, once per week. I only run AVGAS and magneto timing was performed 30 hours ago. I guess I have Champions REM38E and a set of 40E ready to install.

I guess this could come from bad spark plugs, but in a few posts I read a few different reasons and I am a bit confused.

Thanks.
Camillo

[Auburntsts]

Camillo,
It's very difficult to impossible to get a non-fuel injected engine to run LOP. Since you say you're running an O-320 my guess is it's probably your induction system which means you're most likely stuck running ROP.

[turbo]

i have a O-360 experimental engine from lyc thunderbolt with flowed heads. when i lean it there is no roughness. unfortunately i dont have enough engine monitoring to try lean of peak but it will lean to the point of the engine quitting with no engine roughness. thats it.

[jetdriven]

A couple of tricks you can try is to pull the throttle back just slightly to have the throttle plate induce some turbulence and improve atomization. Another trick is a touch of carb heat. One or both of these might allow you to run leaner before the onset of roughness. If you are below ~9.5 GPH (~75% power), all CHT are below 380-400, and it is smooth, you are not hurting it.

[N941WR]

As the others have said, carbureted engines don?t like to run lean of peak.

However, I can do it but only because I have dual electronic ignition (P-mags). Also, you are supposed to only run LoP up high and at or below 65% power.

Typically, with mags, you have to run rich of peak.

[Camillo]

So, I have to resign. Important thing I learnt is that this is normal for a carbureter engine!
Thanks.
Camillo

[jetdriven]

Originally Posted by N941WR

As the others have said, carbureted engines don?t like to run lean of peak.

However, I can do it but only because I have dual electronic ignition (P-mags). Also, you are supposed to only run LoP up high and at or below 65% power.

Typically, with mags, you have to run rich of peak.

They say that but we run 85% power LOP, and TN Bonnaza guys run 95% power LOP. Its all about CHT

[N941WR]

Originally Posted by jetdriven

They say that but we run 85% power LOP, and TN Bonnaza guys run 95% power LOP. Its all about CHT

But both the Bo and your Mooney 201 are injected and the Bo has a Conti engine, which may make a difference.

You are correct, it is all about CHT's but it is also about how rough the engine runs and fuel distribution with a carb is an issue. Thus, if you run lower % power, there is very little chance of damaging the engine.

With my O-360 powered RV-9, I can run it at 155 KTAS LoP while burning around 6.6 GPH. That is way down the power curve. But, I will only do this at 8000’ or above.

[Auburntsts]

There's nothing wrong with running LOP down low as long as you stay below 75%. Flying high just makes the management for normally aspirated engines easier because the mixture setting danger zone (aka the red box) gets smaller with altitude because HP natually drops until the danger zone disappears altogether.

[jetdriven]

Fuel injection makes it much easier. My regular pilot friends freak out when I run 29" MP, 2200 RPM, and pull the mixture to 7 GPH (~150 LOP)

or 11 GPH. (83%)