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Mixture question on first time start

larrys

Well Known Member
First time starting it up yesterday.
We are building an RV14A with a Lycoming 390 Thunderbolt with duel Pmags and standard injection that comes on the motor.

We read the Lycoming manual and followed the steps.

In general it worked very well. But in order for it to run smooth the mixture needed to be moved a lot to accommodate the engine speed. It order to rev it up it needed more mixture. And the same with idle. But in the end it did run very smooth once it was adjusted for the range of speed. We live at 7000 elevation but it's a plane so it should not matter.

We have not done a fuel flow test yet but it measured fuel flow on the AFS screens and the pressure looked reasonably. And when the electric pump was on it seemed to pump too much pressure and you can hear it working well.

The question is it seems that it wants to run very lean and an adjustment is needed in the mixture/flow/pressure to allow for RMP/speed. On other injected planes I have flown the mixture "knob" is out about 1" + - and it just runs (at least at first rolling on the ground and starting run up). In our plane the mixture is about 1/2" from full off. And it constantly needs to be adjusted just to run well.

Does anyone have ideas to try?
Thanks, Larry
 
broken in

First time starting it up yesterday.
We are building an RV14A with a Lycoming 390 Thunderbolt with duel Pmags and standard injection that comes on the motor.

We read the Lycoming manual and followed the steps.

In general it worked very well. But in order for it to run smooth the mixture needed to be moved a lot to accommodate the engine speed. It order to rev it up it needed more mixture. And the same with idle. But in the end it did run very smooth once it was adjusted for the range of speed. We live at 7000 elevation but it's a plane so it should not matter.

We have not done a fuel flow test yet but it measured fuel flow on the AFS screens and the pressure looked reasonably. And when the electric pump was on it seemed to pump too much pressure and you can hear it working well.

The question is it seems that it wants to run very lean and an adjustment is needed in the mixture/flow/pressure to allow for RMP/speed. On other injected planes I have flown the mixture "knob" is out about 1" + - and it just runs (at least at first rolling on the ground and starting run up). In our plane the mixture is about 1/2" from full off. And it constantly needs to be adjusted just to run well.

Does anyone have ideas to try?
Thanks, Larry

seems like it is not broken in and there is a lot of oil in the combustion chamber. i think you are trying to keep the plugs from fouling with all that oil in there. i would see if it improves in subsequent runs. I would expect to see a noticeable improvement on the second and third run prior to first flight. But I think Lycoming recommends to keep ground runs to a minimum.
 
Congratulations!!!

First time starting it up yesterday.
We are building an RV14A with a Lycoming 390 Thunderbolt with duel Pmags and standard injection that comes on the motor.


Thanks, Larry

Larry, congrats on this latest milestone.

I remember talking to you about hangars 6 or 7 years ago and telling you about the RV line.

Glad you are making forward progress on the project.
 
Idle Mixture may be too rich...

Many Lyc experimental engine arrive with the FI system idle mixture adjusted too rich, might explain why your have to lean so aggressively to get her to run. I have experienced this on several projects including two of my own.
+1 on clearing preservative oil from induction system too.:)
 
I had the exact same issues you are describing and know of 3 others who have. For some reason Lycoming after test running is changing the orientation of the idle mixture arm and then reassembling it. It cannot get in the wrong position without undoing the cotter pin and clevis. For me it was as simple as undoing the clevis, readjusting the arm in the correct orientation, reinstalling the clevis, and resetting the idle mixture. The attached picture is before it is corrected, I unfortunately don't have a pic of after, I have drawn in the proper location in black.
I have a Avstar servo and could not keep the engine running without changing the mixture and throttle at the same time. I spoke to both Avstar and Lycoming and they confirmed the problem. I would suggest looking at your orientation of your idle mixture arm and then talking to Lycoming before doing anything else. If not you will drive yourself crazy trying to find the fix.

Here is who I spoke to:
Brandon Dildine
Field Service Technical Representative
Lycoming Engines, an unincorporated operating division of Avco Corporation
[email protected] +1 570-327-7279 or +1 877-839-7878


Rene Loew
AVStar Fuel Systems, Inc.
1365 Park Lane South
Jupiter, Florida 33458
Voice (561) 575-1560
Fax (561) 575-0795
[email protected]
 

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I am so grateful to you all!

I was reading on VAF about another person wondering what brand and type of aircraft to start work on.

With this brain trust is there any doubt! VANS!
 
I was reading on VAF about another person wondering what brand and type of aircraft to start work on.

With this brain trust is there any doubt! VANS!

Can you let us know what you find? I would be curious to know if it is the same issue I had.
 
What are you saying?

I had the exact same issues you are describing and know of 3 others who have. For some reason Lycoming after test running is changing the orientation of the idle mixture arm and then reassembling it. It cannot get in the wrong position without undoing the cotter pin and clevis. For me it was as simple as undoing the clevis, readjusting the arm in the correct orientation, reinstalling the clevis, and resetting the idle mixture. The attached picture is before it is corrected, I unfortunately don't have a pic of after, I have drawn in the proper location in black.
I have a Avstar servo and could not keep the engine running without changing the mixture and throttle at the same time. I spoke to both Avstar and Lycoming and they confirmed the problem. I would suggest looking at your orientation of your idle mixture arm and then talking to Lycoming before doing anything else. If not you will drive yourself crazy trying to find the fix.

Here is who I spoke to:
Brandon Dildine
Field Service Technical Representative
Lycoming Engines, an unincorporated operating division of Avco Corporation
[email protected] +1 570-327-7279 or +1 877-839-7878


Rene Loew
AVStar Fuel Systems, Inc.
1365 Park Lane South
Jupiter, Florida 33458
Voice (561) 575-1560
Fax (561) 575-0795
[email protected]

Correct me if I am wrong, with the "incorrect" orientation, the mixture works backwards, it goes lean as the throttle is opened; the reorientation you describe reverses the shaft rotation as the butterfly is opened. Is that what you are saying? How does one know if the orientation, and linkage length are correct? or better yet, how does one set the orientation and linkage length?

Please help. i am going to be here in a few weeks.
 
I personally know 2 people who had this reversed arm issue to the point where it was so rich even full lean on the idle adjuster was not enough until the arms were corrected by Avstar.
 
Correct me if I am wrong, with the "incorrect" orientation, the mixture works backwards, it goes lean as the throttle is opened; the reorientation you describe reverses the shaft rotation as the butterfly is opened. Is that what you are saying? How does one know if the orientation, and linkage length are correct? or better yet, how does one set the orientation and linkage length?

Please help. i am going to be here in a few weeks.

No the linkage in the wrong orientation will not make the mixture backwards. It only throws the curve out considerably is what I was told. There is only two orientations it can be, one shown in the picture of it aft and one very close to down vertically. The length is determine by adjusting the idle mixture. To do this you want about a 30 - 50 rpm rise with the engine at idle and warm when you slowly pull the mixture out allowing it to shut down.
If the arm is in the aft orientation as shown in the pic reach out to Lycoming prior to adjusting anything.
 
Just following up on the post. Here attached is a picture of the proper orientation of the mixture arm with the throttle closed. Note that it can only be in one of two positions. The wrong position is facing aft and the correct position facing down as shown.
 

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Just following up on the post. Here attached is a picture of the proper orientation of the mixture arm with the throttle closed. Note that it can only be in one of two positions. The wrong position is facing aft and the correct position facing down as shown.

I ran over to check but the arm is in the correct position. There is not enough adjustment to make a difference. So suspecting the snuffle tube valve?
Will update when it is figured out
Larry
 
update - please HELP!

Well, I tried the linkage down then sideways like the pictures, tried adjusting the star between the throttle and mixture every which way, Tried anything we could think of.
The mixture just is not right. Starts OK with a bit of pump when cold with mixture off and a little throttle. but once it warms up it is super lean to idle and you need to move the mixture up with the throttle to get a really good response with no stumble. It is like it has no "accelerator pump" like you would have on a carburetor.
We even tried a scope down the intake to see if anything was weird, it looked clean and new. Took off the sniffle valve at the bottom of the intake and it is new and works correctly.

When the mixture is adjusted to the RPM it runs incredible well. But the mixture can't be set without adjustment for differing RPM. It idles great when adjusted, mid range is great once adjusted and high end runs great when adjusted.

Hopefully someone can HELP!!!
Larry
 
Well, I tried the linkage down then sideways like the pictures, tried adjusting the star between the throttle and mixture every which way, Tried anything we could think of.
The mixture just is not right. Starts OK with a bit of pump when cold with mixture off and a little throttle. but once it warms up it is super lean to idle and you need to move the mixture up with the throttle to get a really good response with no stumble. It is like it has no "accelerator pump" like you would have on a carburetor.
We even tried a scope down the intake to see if anything was weird, it looked clean and new. Took off the sniffle valve at the bottom of the intake and it is new and works correctly.

When the mixture is adjusted to the RPM it runs incredible well. But the mixture can't be set without adjustment for differing RPM. It idles great when adjusted, mid range is great once adjusted and high end runs great when adjusted.

Hopefully someone can HELP!!!
Larry

If the linkage is down as shown in Post #11 and the mixture wheel is adjusted somewhere close to the same and you are still having issues than its likely time to call Lycoming.
 
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