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EGT only goes down while leaning??

C

captainrichhill

Member
RV 6A LYCOMING o320 160HP. Fixed Prop.

I did a long trip recently after having 4 new cylinders installed. I cruised at 7000 and 6000. The EGT temps on the cyls were about 1250 for the back two and 1175 for the front two cyls. At altitude I started to lean while monitoring the #3 cylinder (the hottest). The temp started to decrease as soon as I started leaning. It never peaked. I eventually stopped when I felt the engine getting a little rough. And I pushed the mixture back to the RICH position and only leaned a little and left it alone.
Any ideas on how this could happen? Induction leak? I just had my mags rebuilt because we thought that might have been the cause. But it still seems to be the same issue after the mags has been rebuilt.
Any ideas will be helpful because I don't have any other ideas.
Thanks
Rich
 
What are egt and cht values during take off? You could be near detonation cause too lean at high power. If efis equiped try to record engine parameters.
 
Looking at the last thing changed is usually the best start. I assume it was running fine before the cylinder change? If so I would expect a leak either at a cylinder intake or the carb attachment, assuming it came off at some point.

Chris
 
Do the other cylinders peak? If the temp drops from full rich as you lean, you are apparently running at or lean of peak to start with. It could have to do with the carb jetting, but more likely an induction leak. Did you replace the intake pipe gaskets and rubbers?
 
captainrichhill said:
RV 6A LYCOMING o320 160HP. Fixed Prop.

I did a long trip recently after having 4 new cylinders installed. I cruised at 7000 and 6000. The EGT temps on the cyls were about 1250 for the back two and 1175 for the front two cyls. At altitude I started to lean while monitoring the #3 cylinder (the hottest). The temp started to decrease as soon as I started leaning. It never peaked. I eventually stopped when I felt the engine getting a little rough. And I pushed the mixture back to the RICH position and only leaned a little and left it alone.
Any ideas on how this could happen? Induction leak? I just had my mags rebuilt because we thought that might have been the cause. But it still seems to be the same issue after the mags has been rebuilt.
Any ideas will be helpful because I don't have any other ideas.
Thanks
Rich
Click to expand...

Instad of going to full rich when engine gets rough, push the mixture forward just far enough to get smooth operation and let be there a while and stabilize. Then take a look at temps. It takes a while for things to settle down.

You may not have a problem except normal carb fuel delivery to cylinders. It is never equal. Back in old days before fancy EGT stuff, thats how it was done. Engines ran just fine. Just keep it rich enough to be smooth. No one ever cared about unequal fuel delivery.

When Fi came along that could be controlled and EGT systems were used. But with carb no EGT except maybe on one cylinder. The full EGT information is frustrating with full read out because there is nothing pilot can do about it with a carb.

Keep it running smooth and enjoy flight, don't go nuts trying to balance EGT's with carb.
 
I would say you are running lean at the full rich position and that is why they go down and not up. Do you know what the peak EGT's were before? 1250 seems low, but that number is unique to each setup. I also would speculate on an induction leak somewhere, but if no cylinders peak, then your lean problem is more likely a sump leak near the carb or an issue with the carb not delivering enough fuel.

Larry
 
Have you checked;

1. full travel of the mixture lever at the carb vs. mixture control knob/cable travel

2. correct travel direction
 
First, as Mike said, check travel and directions. Then.
1. Do you get an rpm rise at idleish or slightly above when leaning? (you should)
2. What are the other cylinders doing at full power when leaning? Dont look at just one, look at them all. Do they all rise or all lower?

You can work all this on the ground. No need to do any flying.
 
I have the same problem

I have a KS Avionics EGT/ CHT gauge and I noticed that it did the same thing! I bought the plane about 70hrs ago and from the beginning, I always leaned by sound/ feel. I know it's not very precise, but seemed to work well (or at least good enough).

Recently I tried using the EGT to lean and was surprised to see it DROP instead of rise when I leaned and the opposite when I pushed to rich. Is it possible that somehow the gauge is hooked up incorrectly and that could cause this??

From what I understand the KS units only read relative temperatures (how one cylinder compares to the others) - not absolute, actual temperatures of the gases and cylinders.
 
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