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Old 04-06-2016, 06:08 PM
Jbon Jbon is offline
 
Join Date: Nov 2015
Location: DFW
Posts: 55
Default Running Too Lean?

Well, I know my idle mixture is too lean, because I'm seeing no rise in RPM on shut down. Unscrewing the mixture screw doesn't help, so I suspect there's an issue with the mixture circuit. The the carb is headed to the shop to have this checked out.

The company who sells my electronic ignition system, Electroair, thinks I'm running too lean overall, this based on a large drop of 150-175 RPM at run up. The drop on the single left mag is only 50.

I've checked for an induction leak. . . no joy.
I've changed the plug wires. . . no joy.
I've swapped the upper/lower spark plugs. . . no joy.
I've checked the EIS timing. . . perfect.

So, I assumed there may be an issue with the EIS itself, perhaps a bad coil. They don't think so, especially since my plugs are so clean. They're saying that lean mixture roughness will be apparent on the EIS but not the mag because of the higher efficiency and longer spark duration of the EIS.

I Figure since I'm sending the carb to the shop to investigate the idle circuit leanness, I might as well wait and see if something else shows itself.

The carb shop tells me that a number of their customers have had their overall mixture richened by drilling out the main jet ten-thousands. I'm not sure mine needs this, but I'm pretty sure its not running overly rich either. My plugs appear pretty light gray. . not sure if it's light enough to indicate an over-lean condition, but I'm going to get the carb shop to look at it. I'm not really seeing excessively high EGT, but I've only got about 10 hours on the airplane, and I always aggressively lean in flight, so I can't say for sure. Oil temps could probably be higher. I run near the bottom of the green.

So what's the harm of having the carb richened a bit. Has anyone done this? I figure I can still use the mixture knob to lean where I need to be, but is there any downside to doing this?

Thanks!
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  #2  
Old 04-06-2016, 06:26 PM
MikeS MikeS is offline
 
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Sounds like things are fine from your description. Perhaps the Electroair system needs some adjustment to their advance or some other tweak (not familiar with Electroair) . . . instead of calling the drop the fault of your induction system.

Lean is good. Lean is cool. Except when pulling 75% or more on takeoff and climb when the excess fuel is used . . . not for optimum combustion but for cooling. I think the reason for the drop lies with Electroair, not your engine as it is currently set up.

My two cents.
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  #3  
Old 04-06-2016, 10:05 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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You need some holistic advice and support here. You are kind of all over the map. My comments in line below.

Quote:
Originally Posted by Jbon View Post
Well, I know my idle mixture is too lean, because I'm seeing no rise in RPM on shut down. Unscrewing the mixture screw doesn't help, so I suspect there's an issue with the mixture circuit. The the carb is headed to the shop to have this checked out.

How do you know it's too lean. Does it idle rough and want to die? Do you get a stumble when accelerating from idle? If no to both, you are not too lean. The test you mention is a guideline. Most experts will tell you that you should only be rich enough to achieve a smooth idle and avoid acceleration stumble and lean enough to avoid plug fouling.

The company who sells my electronic ignition system, Electroair, thinks I'm running too lean overall, this based on a large drop of 150-175 RPM at run up. The drop on the single left mag is only 50.

This guidance makes no sense to me. RPM drop amount should change very little between rich and lean conditions and won't affect the two ignitions differently; Certainly not enough to explain your difference. Use the search here. Many have very similar numbers to those that you are posting. Most of the difference is likely due to the fact that the timing is different for the two systems at your runup speed/RPM. timing advance directly impacts RPM at any given throttle/mixture combination, especially noticeable at idle and lower RPMs. The electroair is changing the advance dynamically and is likely not the same 25* that your mag is set to at your runup RPM.

Further, above you talk about idle mixture being lean and here, at these RPMs, your talking about main metering. Carbs have completely different circuits for idle and main fuel metering.

I've checked for an induction leak. . . no joy.
I've changed the plug wires. . . no joy.
I've swapped the upper/lower spark plugs. . . no joy.
I've checked the EIS timing. . . perfect.

So, I assumed there may be an issue with the EIS itself, perhaps a bad coil. They don't think so, especially since my plugs are so clean. They're saying that lean mixture roughness will be apparent on the EIS but not the mag because of the higher efficiency and longer spark duration of the EIS.

This also doesn't make sense the more powerful spark should be MORE tolerant of the lean condition, not less. Very lean mixtures are harder to light and a stronger spark will allow a leaner mixture to fire off more consistently than a weak spark. However, as I mention below it is quite unlikely that you are running Lean at 1800 RPM, if the red knob is at full rich. These carbs are designed to run rich. This you can test quite easily by leaning at 1800 and observing your EGTs.

I Figure since I'm sending the carb to the shop to investigate the idle circuit leanness, I might as well wait and see if something else shows itself.

The carb shop tells me that a number of their customers have had their overall mixture richened by drilling out the main jet ten-thousands. I'm not sure mine needs this, but I'm pretty sure its not running overly rich either. My plugs appear pretty light gray. . not sure if it's light enough to indicate an over-lean condition, but I'm going to get the carb shop to look at it. I'm not really seeing excessively high EGT, but I've only got about 10 hours on the airplane, and I always aggressively lean in flight, so I can't say for sure. Oil temps could probably be higher. I run near the bottom of the green.

You may or may not need to drill your jet. Many RV'ers need to drill their jets to get proper fuel flow in WOT conditions. I did. However, you have not posted any data. Use the search. This subject has been addressed at great length. Be advised, drilling the jet will increase fuel across the range from just off transition to WOT and will waste fuel when you don't lean. However, the decision point is whether or not you have enough fuel at WOT to get into the 150-200 ROP range. This can only be adjusted by increasing the size of the jet. It is quite unlikely that you are lean at mid-throttle RPMs. These carbs have many flaws, but I have not seen anyone complain of lean mid-throttle conditions.

So what's the harm of having the carb richened a bit. Has anyone done this? I figure I can still use the mixture knob to lean where I need to be, but is there any downside to doing this?

The harm is in reduced power. Overly rich mixtures reduce power, in addition to wasting fuel. Better to make this decision to drill the jet based upon data, not hunches or a mixed bag of advice.

Thanks!
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Last edited by lr172 : 04-07-2016 at 07:30 AM.
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  #4  
Old 04-06-2016, 11:35 PM
RV10inOz's Avatar
RV10inOz RV10inOz is offline
 
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Quote:
Originally Posted by MikeS View Post
Sounds like things are fine from your description. Perhaps the Electroair system needs some adjustment to their advance or some other tweak (not familiar with Electroair) . . . instead of calling the drop the fault of your induction system.

Lean is good. Lean is cool. TRUE when LOP Except when pulling 75% or more on takeoff and climb when the excess fuel is used Again, when LOP it is fine, but takeoff and climb are generally better done ROP, full rich and a target EGT in the climb. . . . not for optimum combustion but for cooling. Completely false, the extra fuel is for optimum combustion otherwise the ICP's rise and that drives up the CHT. I think the reason for the drop lies with Electroair, not your engine as it is currently set up.

My two cents.
Just thought I would fix it up a bit for you, I know you had the right intentions, but the delivery needed refining.
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  #5  
Old 04-06-2016, 11:36 PM
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RV10inOz RV10inOz is offline
 
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JBON,

What is your takeoff fuel flow MP and RPM, do you have an ems and can upload the data?
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  #6  
Old 04-07-2016, 09:00 AM
Kent Ashton Kent Ashton is offline
 
Join Date: May 2010
Location: Concord, NC
Posts: 116
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No engine expert here but I believe the idle mixture check you're concerned about is there just to insure that the engine is not running so lean or so rich at idle and full rich selected, that it could quit on you. Had that happen on base once when the idle mixture was set too lean. :-(

Drilling out jets to enrich the mixture is something else. If at cruise RPM and full rich, the RPM did not rise as you leaned from full rich but immediately begins to drop off, then you might suspect you were jetted too lean.

Last edited by Kent Ashton : 04-07-2016 at 05:25 PM.
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  #7  
Old 04-07-2016, 02:01 PM
MikeS MikeS is offline
 
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Again, from your plug colors and other description of engine operation, I wouldn't change anything at this point. The "problem" is an excessive drop on the electronic ignition. It is there I would look. It's not firing at the proper time in the combustion cycle. Should be an easy adjustment, but I know nothing of that particular system. I'd leave your jets alone for now.
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  #8  
Old 04-08-2016, 08:12 AM
Jbon Jbon is offline
 
Join Date: Nov 2015
Location: DFW
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Quote:
Originally Posted by lr172 View Post
You need some holistic advice and support here. You are kind of all over the map. My comments in line below.
I agree that it doesn't make any sense that the EIS would be more sensitive to a lean condition. I've never been able to wrap my head around that concept.

I'm aware that the idle circuit is not a player at run up RPM, but it is pretty clear to me that there is an issue with the idle circuit. Turning the mixture screw out 5 or so turns should make a difference in idle mixture. With mine, it does not.

I think it's good advice not to do anything with the main jet until I have more data, so I'm putting that off. I have pulled the carb and sent it to the shop to have it looked over. Given that it hasn't been looked at for over 18 years, that seems prudent.
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  #9  
Old 04-08-2016, 08:16 AM
Jbon Jbon is offline
 
Join Date: Nov 2015
Location: DFW
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Quote:
Originally Posted by RV10inOz View Post
JBON,

What is your takeoff fuel flow MP and RPM, do you have an ems and can upload the data?
No fuel flow gauge (yet), and no EMS. Once I get this ignition issue resolved and I'm back in the air, I'm going to take a closer look at the engine's response to mixture. The airplane is new to me, so I don't have a lot of data.
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  #10  
Old 04-08-2016, 12:48 PM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by Jbon View Post
I agree that it doesn't make any sense that the EIS would be more sensitive to a lean condition. I've never been able to wrap my head around that concept.
I offer that engines with electronic ignitions are more sensitive to lean conditions at idle than mags, and the more the timing is advanced at idle the more the issue will present itself (based on some personal fuel injector trouble shooting).

To the original issue, are you really sure you have the timing right? For Lightspeed and pMag I know the timing is set at Top Dead Center (TDC) - not 25 degrees before TDC like a mag. I don't know what Electroair tells you to do.

Is this the first run with the ElectroAir? If so, did the problem exist when running mags?

Carl
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