New owner leaning question

[Hector]

Promise will give it a try within next 48 hours. Tried to do it today, but wife had other ideas.

[Hector]

OK, consider this an interim PIREP (I'll explain later). Went flying after work today in an attempt to see if my carbureted C could be run LOP with my relatively new JPI 730. Leveled at 6500, 22" MP, and 2400 RPM ( this is my typical cruise setting). As a baseline I first tried leaning to my usual 20 degrees ROP which yielded around 9.6 GPH. I repeated this three more times with the same results regarding fuel flow, however, in three of the four attempts a different cylinder peaked first. I had noticed this in the past but was not sure what to make of it. Not sure what it means but I would rather think that my fuel distribution is probably pretty good for a carburetor. Next, I set the JPI in LOP mode and started leaning. The first cylinder peaked and went lean quickly followed by two more cylinders, but before the last cylinder went lean I started to feel a little roughness. By the time the last cylinder went LOP my fuel flow was 7.3 GPH. I had to enrich to a fuel flow of 8 GPH to eliminate all signs of roughness. I tried this 3 more times with similar results, just before or at the same time the last cylinder goes LOP I start to feel some roughness between 7 and 7.5 GPH, enriching to about 8 GPH clears the roughness AND CHTs were about 20 degrees cooler than when leaned to 20 degrees ROP (350 vice 370). So what does this all mean???? Well for one thing it looks like the method I was using before I got the JPI (lean to roughness and enrich a little) is probably the best method and I just wasted a bunch of money on a 730. Just kidding, glad to have the engine monitor for many obvious reasons. Now for the really stupid lapse of memory, I completely forgot to use carb heat in an attempt to make that last cylinder go lean without roughness. It was late and I was getting tired. So this is an interim PIREP until I try this again this weekend.

[DS1980]

No worries. It's hopeful though since you were so close without using carb heat or closing the throttle plate a little. Just check your POH for power settings that keep you around 60% and you won't hurt anything. 350 degrees for your CHT is excellent. How far apart are the cylinders when it goes smooth at 8 GPH?

 

What power % does the POH say at the cruise settings you use? I'd be careful with the whole lean-to-rough-and-then-back-to-smooth OWT. Of course if you're at 370 degrees you might be ok. But the 350 is better.

[carusoam]

A single cylinder engine always runs rough, or it doesn't run at all.

There is not much balance with a single cylinder...

Best regards,

-a-

[scottfromiowa]

According to a well known upper midwest MSC, under new ownership....."running lean of peak will wear out a set of cylinders on a J inside of 100 hours". .....the stupidity continues with the following statement "camguard is no good the last plane I changed oil on that had cam guard in it all the cam guard drained first out of the quick drain"......to be followed up with the dumbest statement I have ever heard especially coming from a MSC owner "LOP doesn't save any gas when you take into account you go slower".....ok wait this guy said one more hillarious comment "a Bravo won't run LOP because the engine is balanced so perfectly that it will only run ROP" .............. I couldn't get my plane out of there fast enough! I mean this guy was actually turning wrenches on my plane! Scary!

Please PM me the service center as I THINK I know what one you are talking about...I wouldn't bring my plane there.

[jetdriven]

According to a well known upper midwest MSC, under new ownership....."running lean of peak will wear out a set of cylinders on a J inside of 100 hours". .....the stupidity continues with the following statement "camguard is no good the last plane I changed oil on that had cam guard in it all the cam guard drained first out of the quick drain"......to be followed up with the dumbest statement I have ever heard especially coming from a MSC owner "LOP doesn't save any gas when you take into account you go slower".....ok wait this guy said one more hillarious comment "a Bravo won't run LOP because the engine is balanced so perfectly that it will only run ROP" .............. I couldn't get my plane out of there fast enough! I mean this guy was actually turning wrenches on my plane! Scary!

Post that over on beechtalk, some Bonanza guys have two TBOs on LOP ops, and the same set of cylinders and the same engine.  Factory Continental cylinders wont make TBO because the valves arent machined concentric to the valve seats. Lycoming's arent necessarily like that.

 

We have 180 hours on ours, and even broke it in LOP. Send them that and ask them what they think. Oh, the last annual was at 140 hours, and all the compressions were 78/80. 

[DS1980]

A single cylinder engine always runs rough, or it doesn't run at all.

There is not much balance with a single cylinder...

Best regards,

-a-

 

You're talking about balance, and that's true. The subject was running rough in regard to fuel distribution. And a single cylinder will run wonderfully in between too rich to burn and too lean to burn. My lawn mower, weed eater and model aircraft engines are proof. All single cylinder, all run like a top in between flooding and being starved.

I agree that some vibrate because there are no counteracting forces. This is vibration, different than rough.

[DS1980]

And I agree with everybody Aaronk25, put the name on here. Why protect the guilty? A mechanic will pass his biases onto customers:

"Oh, this guy runs lean of peak. Guess I will have to charge him for new exhaust valves. Oh, lets throw in a cylinder replacement too. My borescope broke but I know it's bad."

[carusoam]

It will be interesting how well a C can run LOP with all the instrumentation and advice that is available....

Carb heat and throttle position, anything else?

At WOT is there additional jetting to be tried or avoided?

If there is, the fuel flow should indicate a step where it comes in.

Good luck,

-a-

[jetdriven]

Apply the 65% rule, below ~8.7 GPH, there is no mixture setting that will harm the engine.  So, pull it to 8.7 or less, watch that it runs smooth, and no cylinder over 380, and roll on. and on.    and on.. .. 

[DS1980]

Carb heat and throttle position, anything else?

 

The use of carb heat and throttle positions are the only methods I know of. Doesn't mean there isn't more. The idea is to maximize the atomization (wow, sounded smart there eh?) of the fuel so that when it enters the intake manifold all of the fuel molecules weigh the same. It won't be perfect, but then again even balanced fuel injectors have a margin of error (I think 0.5 gph). As I stated as well at Byron, keeping the power at or below 65-60% the engine just isn't generating enough ICP to hurt itself.

[Hank]

It will be interesting how well a C can run LOP with all the instrumentation and advice that is available....

Carb heat and throttle position, anything else?

At WOT is there additional jetting to be tried or avoided?

If there is, the fuel flow should indicate a step where it comes in.

Good luck,

-a-

 

Yes, there is automatic fuel enrichment at WOT. That's why I always reduce throttle enough to make the MP needle move before leaning. I only have the factory single-point probes, though, and have been unsuccessful attempting LOP smoothly with varying amounts of carb heat at this slightly reduced throttle setting. At 20"/2500 at 10,000 msl, I am 5-7 mph Indicated slower at peak EGT than at 50ºF rich.

[DS1980]

A perfect execution with a not perfect result. It was worth a shot Hank!

[Hank]

I did make some notes that I left in the plane. I would like to compare with other C owners to see if there really is an effect from my 3-blade and 201-windshield & wingtips. E/F/J owners can read them and laugh, we're all a little slower. Something to do with them having 20 extra ponies under the cowling.

 

But I do always back the throttle off; cocking the throttle body may not actually improve fuel atomization, but it might, too.

[DS1980]

It does. As you stated it "turns off" the enrichment valve ( the Brits call it the economizer, which sounds better) and creates some turbulence in the carb. If you've ever sucked through a straw with a hole in it you can get an idea of what is trying to be accomplished.

[pinerunner]

It will be interesting how well a C can run LOP with all the instrumentation and advice that is available....

Carb heat and throttle position, anything else?

At WOT is there additional jetting to be tried or avoided?

If there is, the fuel flow should indicate a step where it comes in.

Good luck,

-a-

Well ...

 

One thing noone's mentioned is using lower RPMs. That would give more time between the carburator and points where the manifold divides the flow to the different cylinders. If the fuel were completely vaporized and the gaseous fuel/air mixture truly mixed, carburated engines ought to be the easiest to operate LOP instead of harder. Droplets going around corners are expected to be thown to the outside of the curve. Evaporation cools down the droplets and tends to slow down further evaporation. Along with a bit of carb heat and turbulence from the cracked throttle a bit more time might make the difference. The volume per unit time and linear velocity in the manifold will be primarily (perhaps even strickly) a function of RPM so that's the way to give the droplets a little more time to evaporate. I'd try it myself but I've got an M20E so it wouldn't be the same.

 

Stay at lower powers of course; even Mike Busch says he uses 100 ROP if he wants to go fast.

[DS1980]

 If the fuel were completely vaporized and the gaseous fuel/air mixture truly mixed, carburated engines ought to be the easiest to operate LOP instead of harder. This is exactly why some carb engines are difficult to operate LOP. The fuel distribution is not equal to all cylinders. The only reason why we can operate any carbed multi-cylinder engine is because the power curve on the rich side of peak is flat so a difference in fuel flow between the cylinders will not produce a significant difference in power.

 

Stay at lower powers of course; even Mike Busch says he uses 100 ROP if he wants to go fast. ??? Confusion on this statement. LOP has nothing to do with speed. It has to do with engine longevity and running at best economy.

 

There are 2 schools of thought on RPM. The Mike Busch College of Aviation says to use low RPM because it gives the most time for the cylinder to extract power from combustion event. The John Deakin College of Aviation says that using a higher RPM will optimize the Peak of Pressure Pulse to extract the most power from the combustion event. Electronic ignition will probably make the latter obsolete, but for right now with fixed timed magnetos, they are both 50% correct which puts us right back to where we started. Now that's progress, the FAA way!!!

[Hank]

You are so right--LOP has nothing to do with speed. When Mike B. wants speed, he flies ROP, but goes 100 instead of 50 rich to avoid the dreaded Red Box. Even though my C won't run smooth LOP, I lose 8mph Indicated by going from 50ROP to Peak. 100 Rich should be faster, while any LOP will be slower.

Sometimes it really is about speed and time enroute.

[pinerunner]

So, in the end, have any of the carburated folk found a sweet spot where they could run their M20C LOP. It appears the answer is no.

[DS1980]

Results will vary dramatically between pilots. Some will claim they can get most carb engines to run LOP while others say they have about a 30% sucess rate.

I believe most carb engine has that sweet spot, but it's not a very wide spread so finding it can be diffucult. Plus, it can change depending on density and temperature so it won't be as consistant as an injected engine with balanced injectors.

 

But the answer is yes, a carb engine can run LOP smoothly.

[Hank]

"A" carbed engine may run LOP, sometimes. Not all of them. Like injected engines, there are airframe-specific variables. Sometimes a little carb heat helps, sometimes not. Some planes will sometimes, some won't. Mine hasn't so far, and I forgot to experiment today, so maybe tomorrow going home.