RPM gain at idle during leaning

[Dickard]

Like the title says, during idle, after startup, how much RPM increase do you get when you lean?  The Electroair mechanic was here this week (again) and he was surprised at how much RPM increase during lean.  He thinks my fuel system is not set right.  At 800 RPM leaning to peak RPM I end up at about 1050 RPM.

[Shadrach]

19 minutes ago, Dickard said:

Like the title says, during idle, after startup, how much RPM increase do you get when you lean?  The Electroair mechanic was here this week (again) and he was surprised at how much RPM increase during lean.  He thinks my fuel system is not set right.  At 800 RPM leaning to peak RPM I end up at about 1050 RPM.

I see perhaps 50rpm increase. I can’t say for sure what’s normal for a Bravo but a 250rpm increase seems like it’s idling very rich. This reads like your idle mixture is FUBAR. It should be field adjustable. 
 

BTW, nice Avatar!

[Dickard]

1 hour ago, Shadrach said:

I see perhaps 50rpm increase. I can’t say for sure what’s normal for a Bravo but a 250rpm increase seems like it’s idling very rich. This reads like your idle mixture is FUBAR. It should be field adjustable. 
 

BTW, nice Avatar!

I would expect mine to be a little higher than your since I'm at 6200 feet, but 250?  Not so sure.

And thanks. :-)

[Shadrach]

31 minutes ago, Dickard said:

I would expect mine to be a little higher than your since I'm at 6200 feet, but 250?  Not so sure.

And thanks. :-)

Perhaps but I don't see a noticeable delta in rpm rise between seasons and my home drome can have a DA spread as much as 5500 feet when comparing a single digit day in February to a nearly triple digit, high humidity day in August.

[PeteMc]

If the plane is started at full rich at 6K + whatever the DA is with the temps, I could see a pretty good rise in RPMs over what you would see at SL.

I haven't been flying with the high temps, but I see the DA is ~4800 today, so I'll have to pay attention in the hot Wx next time to see how much increase I get. 

 

[jlunseth]

I own a 231, not a Bravo, so take this with that grain of salt. I would ignore the mechanic. First, the average idle rise is 75 RPMs. But so what if you see more? The turbo Mooneys are generally set up to run very rich, and the purpose of that is to keep the engine cool when you use full power settings such as during climb or hot weather operations. That is much more important to engine health than whether the pilot needs to use the red knob more at low idle.  Lots of mechanics who are experienced with NA engines don’t understand that this is different with a turbo engine.

I am not a mechanic, but am told that there are actually three screws for setting fuel flow, and there is some back and forth between them. In other words, if a mechanic sets the full fuel mixture and then sets the idle mixture, it is necessary to go back and check the full fuel mixture to get a balance between the two. Many don’t bother, with the result that the full power fuel flow is low. So yes, more fiddling with the mixture setting might reduce the idle rise that you see. But you can do the same thing with the red knob, just lean it out more at low power. Frankly, you are going to find with some experience with your aircraft that things like how far out you need to lean at idle are going to vary a little each time the engine comes out of annual, where the fuel flows were reset. What is of paramount importance to the health of your engine is that you can get full specified fuel flow at 100% power.

[jetdriven]

231s are set up very rich for takeoff and full power but this doesn’t have much to do with the idle mixture.  You need to setup the fuel injection system per the manual M-0.  Follow the manual with calibrated gauges.  But further.  You want the metered (full power) fuel to be at the top of the range, and the un-metered (idle) fuel to be near the bottom of the range.  Because the Continental Fuel Injection system runs rich in the midrange.  Then, further, set the idle mixture for a 50 rpm rise.   
250 is far too much.  When we installed the electroair it needed a good bit of idle adjustment leaning. The electroair burns all the fuel. 

[Shadrach]

2 hours ago, jlunseth said:

I own a 231, not a Bravo, so take this with that grain of salt. I would ignore the mechanic. First, the average idle rise is 75 RPMs. But so what if you see more? The turbo Mooneys are generally set up to run very rich, and the purpose of that is to keep the engine cool when you use full power settings such as during climb or hot weather operations. That is much more important to engine health than whether the pilot needs to use the red knob more at low idle.  Lots of mechanics who are experienced with NA engines don’t understand that this is different with a turbo engine.

I am not a mechanic, but am told that there are actually three screws for setting fuel flow, and there is some back and forth between them. In other words, if a mechanic sets the full fuel mixture and then sets the idle mixture, it is necessary to go back and check the full fuel mixture to get a balance between the two. Many don’t bother, with the result that the full power fuel flow is low. So yes, more fiddling with the mixture setting might reduce the idle rise that you see. But you can do the same thing with the red knob, just lean it out more at low power. Frankly, you are going to find with some experience with your aircraft that things like how far out you need to lean at idle are going to vary a little each time the engine comes out of annual, where the fuel flows were reset. What is of paramount importance to the health of your engine is that you can get full specified fuel flow at 100% power.

“So what if” is that his Idle mixture is out of spec. His mechanic is likely familiar with the continental fuel system and has identified a potential issue.
I think you’re misunderstanding how the fuel system works. Idle mixture adjustment is independent of full throttle, max manifold pressure, fuel flow. Both are affected by fuel pressure which is affected by engine RPM. Idle fuel pressure is unmetered and is controlled by a low pressure relief valve. High max power fuel flow is metered and is adjusted separately. The system must be set up in the correct sequence. While one aspect of the system can affect another, I think you’re assuming correlations that need not be correlated.
Also, It looks to me like Continental specifies 25-50 rpm rise for all engines except for the IO240B. My review of the manual found nothing about compensating for field elevation during set up, though it’s possible I missed it.

 

[Jetpilot86]

I’ve got a Bravo, and I used to be between 4.5-5gph IIRC on a full rich start.  I’d then lean back to the mid 3’s for peak idle RPM.  Roughly an inch away from full rich.

Now I lean some of that out after priming, but before starting so I’m hopefully running less risk of fouling plugs while on the ground before the run up. I’ll add a few twists rich before the run up and lean again for 2000 at peak rpm for the run up. 
 

Leave the mixture there until I’m back at 2000 RPM, fully richen the mixture for takeoff and then finish adding the throttle in for takeoff. 

I’ll run WOT until I’ve accelerated and am ready to set cruise power at top of climb to provide max FF for cooling in the climb because of my pesky #6 liking to get to the 400°+ area despite a host of corrective measures. 

I’m about to find out what the forum thinks of this.  

[MB65E]

OP has a Bravo. 
That’s a Turbo Lycoming. Not much adjustment on the Lycoming system in the field. 
Completely different injection system than the Continental info people are reciting.
I used to run all FI Lycoming’s with a 200 rpm rise thinking richer was better. More idle fuel just fowls plugs. I now follow the book,  A rise of 50 rpm is a lot. Lean it out a few turns with the adjustment arm/linkage. 
Also, if you can no longer get a rise at 900 RPM when pulling the mixture, the fuel servo needs overhaul as the diaphragm needs replacing. 
Had a similar issue with an E model, couldn’t get a rise during a few oil changes/adjustments. Ended up loosing the engine in cruise at 6500ft…

-Matt