What causes this????

[airguy]

Originally Posted by truflite

Check your air induction tube for that cylinder. Make sure it is not leaking. It could be going well lean of peak which could lower the temp drastically. We had a similar problem on a C182. After a mountain of money, tightening a hose clamp fixed the problem. Won't cost you anything to try it.

Dave Nellis

I disagree - the problem manifests itself at high power, which is high manifold pressure. A leaking induction tube is a possibility, but it would result in a rich-of-peak scenario at high power, not lean. At low power settings it would leak more air into the induction, requiring an abnormally rich mixture to produce smooth running. At high power setting the pressure differential across the leak drops to nil and no additional air comes through, but the mixture is still adjusted on the rich side, producing a mixture rich enough to depress the EGT.

I would suggest leaning the mixture at full power slowly in flight until nearly lean cut-off, and monitoring that EGT/CHT - that may tell you a story.

[AZtailwind]

Originally Posted by truflite

Check your air induction tube for that cylinder. Make sure it is not leaking.

I disagree with Airguy- Always check the induction tubes anyway-
They will be sucking excess air- not fuel (lean of peak condition and rough running that will lesson on power reduction) Been there done that-

I also see this minor rough running in a full power takeoff on our 6A- Also have a carb with dual mags on a CS speed 0360- I also attribute this to the excess and unequal fuel distribution with a full power to one or two of the cylinders. The experiment was to pull a little power after initial climb and it smooth’s out to a happy power setting- Also adjust mixture early in the climb at around 3,500 or lower for my engine/carb combo- doesn't take much leaning to smooth this out- So I think your EGT drop is excess fuel in that #2 Cyl. One of the the plug conditions at high pressure may also be it.
my .02$. Let us know what you find!

[airguy]

Originally Posted by AZtailwind

I disagree with Airguy- Always check the induction tubes anyway-
They will be sucking excess air- not fuel (lean of peak condition and rough running that will lesson on power reduction) Been there done that-

I also see this minor rough running in a full power takeoff on our 6A- Also have a carb with dual mags on a CS speed 0360- I also attribute this to the excess and unequal fuel distribution with a full power to one or two of the cylinders. The experiment was to pull a little power after initial climb and it smooth’s out to a happy power setting- Also adjust mixture early in the climb at around 3,500 or lower for my engine/carb combo- doesn't take much leaning to smooth this out- So I think your EGT drop is excess fuel in that #2 Cyl. One of the the plug conditions at high pressure may also be it.
my .02$. Let us know what you find!

Ok, now I'm confused - you say you disagree with my logic (lean vs rich on #2) but yet you come to the same conclusion I did for the same scenario (rich on #2)? If the induction tube is leaking, it's going to leak MORE at low power (low manifold pressure, more air being sucked in) and create a lean condition. If the carb is initially set up to produce smooth operation at this point (which it obviously would be on a new install), then you would not necessarily realize you had an induction leak. At high power (high manifold pressure) there is no pressure differential to drive that additional air through the leak, and the mixture is now excessively rich. This is not a condition that would be easily recognized on the ground, but would manifest itself at full power in the air.

I was not disagreeing about the induction tube being a possible problem point - but rather the result of that leak being a rich condition rather than a lean one (at WOT).

[Brantel]

How would the enrichment valve system play into this situation???

My carb was purchased from a man who bought it several years ago new with an engine that he bought from Aerosport. He stated that he pulled it off the engine and installed FI before ever running the engine and the carb sat on the shelf for several years. He also stated and it was confirmed by Bart at Aerosport that the carb was modified to richen it up for better use on an RV.

When I got the carb, I opened it up and cleaned it and changed the float and also checked that the main jet was truly larger than a stock 10-3878 and it was.

I cleaned everything very well and put it all back together.

I did not tear into the enrichment valve area since it had a lead seal on it.

Could the enrichement valve be plugged or blocked open?

I am not going to get too worried at this point since the engine is a new rebuild with about 30 minutes of flying time on it. It is running mineral oil at this time and I doubt it is even close to broke in yet.

The fuel flows are about what I would expect for a FP 180hp engine on that day and pressure altitude so I do not think it is running too lean. I have no idea if the fuel flow sensor is accurate yet as it only has the Dynon default K-factor in the EMS at this time. After I get some fuel burned, I can check to see how close it is to actual.

Thanks for all the help.. I am stuck up here in Augusta WI for this week and all I have to do is think about flying my new airplane!!!!

[AZtailwind]

Originally Posted by airguy

Ok, now I'm confused - you say you disagree with my logic (lean vs rich on #2) but yet you come to the same conclusion

Hay Greg, I agree with your conclusion
it is probably not a leaking induction tube-
It may be a rich unbalanced nature of #2 Cyl getting a little too much fuel. My 6 does the same thing though I have not investigated it with an EM.

I disagree that induction problems cause a fuel rich of peak issue: your first post stated induction leakage is ?a rich of peak issue? you probably meant lean of peak?
This is from experience: An induction leak will make the roughness across the whole power band with a lower power setting being the smoothest. Almost as bad as if you lost a cylinder. The lean cylinder or cylinders will be lean of peak and running hot. It can be an expen$ive leak!I was just saying this was something to allways check but probably not the issue.

Also for Brantel- RV?s do get a little more MP/Power due to the ram air effect of the racing style air intake. Though I?m not sure is it deserves a larger main jet to ballance and increase of +2 MP at high cruse(??). You are getting into the art/science of carburetors here- maybe a call to Malon is in order. Or maybe it is a spark plug?

[NDrv8r]

Have you looked at something as simple as a bad connection, bad crimp in an egt wire?

It might have reasonable connection until the vibration at max power comes in and then the system is averaging the noisy data.

[az_gila]

Originally Posted by NDrv8r

Have you looked at something as simple as a bad connection, bad crimp in an egt wire?

It might have reasonable connection until the vibration at max power comes in and then the system is averaging the noisy data.

...EGT probes and see if the problem moves with the probe.

[airguy]

Originally Posted by AZtailwind

I disagree that induction problems cause a fuel rich of peak issue: your first post stated induction leakage is “a rich of peak issue” you probably meant lean of peak?
This is from experience: An induction leak will make the roughness across the whole power band with a lower power setting being the smoothest. Almost as bad as if you lost a cylinder. The lean cylinder or cylinders will be lean of peak and running hot. It can be an expen$ive leak!I was just saying this was something to allways check but probably not the issue.

On an airplane with a properly adjusted carb (or injector) such that the mixture is correct, and THEN an induction leak occurs, yes I would agree with your statement.

In this case however, my premise was that the induction leak could be present from the first start and was not recognized. The carb was set up to result in smooth running at ground-power levels (where additional air is being drawn into the tube post-carb), which would result in a slightly over-rich mixture if the induction leak was not present. At full power the manifold pressure is essentially the same as atmospheric and the leak is essentially zero, which would result in a richer mixture than desired. If you are already running a full or nearly-full rich mixture (as you certainly would on engine break-in during Phase I) then this could very well be rich enough on one cylinder to drop the EGT.

I would also think however, that for my scenario to be true, the leak would need to be at the throttle body and not one individual cylinder, in order to get the engine to idle smoothly with the leak present.