Plug fouling on one magneto only?

[Andrew K]

During prolonged taxi with leaning, lately I get a bigger drop during the runup on one magneto with a little roughness when compared to the other. If I lean it out for 30 seconds and try again it is as smooth as can be again which leads me to believe it is most likely just plug fouling right?

Is it normal for one side to foul more than the other on a semi-consistent basis? If not, what are some things I can look at to help find and correct the cause?

Thanks guys!

[joewcasey]

My left has a tendency to fowl more consistently than the right. I've owned it for almost 4 years, mags always check out good, and even continued to do it after my engine was re-honed and re-ringed. Usually happens about every 25-30 hours.

[andya]

even with leaning after start and all ground ops I find the plugs still get some lead in them after 25-45 hours. this could be part of the problem. I used to use that additive in the gas but it is a hassle and expensive but that minimize the lead quite a bit. Alcor something or other. Mind is going fast.... sorry

[Lownslow]

From my experience, there are a couple of things to consider. You may be pulling some oil by the intake valve guides at low MAP (low RPM conditions) if you happen to have high time cyls. You may have this condition and your compression be very good. It may be just one cyl causing the mag drop on these 4 cyls. You may be able to use a (hotter) spark plug that retains heat which helps burn the oil away. The leaning does this as you have described. I believe that if that you are using the 38E plugs you can go to the 40E plugs, but you should verify that before you count on this info. You can speak to a reputable mech about this. Lycoming cylinders last a long time if taken care of, but depending on time in service and the quality of work when the cyll valve train was overhauled, you may have a valve guide leakin oil.

Lou S.

[59pacer]

I have an O-200 in one of my aircraft that has issues that I need some advice on.
On #2 cylinder both plugs get significant carbon fouling--not burnt oil but just dry black 'smoke'. Just like that cylinder is running very rich. It's particularly bad after a long taxi (I lean hard while taxiing) and gives excessive mag drop and rough running during run up. The upper plug seems to be the worst affected of the two.
If I take off and fly the engine runs fine.
I've swapped plugs and the leads check out fine. All the plugs have a resistance of about 1000ohms.
The REM40E is specified for the engine, or fine wire types.
I understand that the mixture strength will vary between cylinders, but this seems excessive.
Any thoughts anyone??

[Steve Pierce]

Time on the cylinder, engine? Look good via borescope? One piece venturi in the carb? History on carb? Might be good to have it flow tested. I would install fine wire plugs in that cylinder and see what happens.

[59pacer]

Time on the cylinder, engine? Look good via borescope? One piece venturi in the carb? History on carb? Might be good to have it flow tested. I would install fine wire plugs in that cylinder and see what happens.

Thanks, Steve. The engine was completely overhauled about 300 hours ago, as was the carb. Compressions and oil burn are fine. I'll check the venturi and borescope next visit. My next thought was to try fine wire plugs also.

[JPerkins]

Random thought. Check your primer system, if it has one and has a nozzle on that cylinder. If the primer pump isn’t sealing it could be sucking fuel through the primer lines and for whatever reason most of it is getting drawn into that cylinder. Another thing could be a cracked primer line that low manifold pressure during taxi is allowing residual fuel to get ingested.


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[59pacer]

Good thought. I'd had that problem as a junior instructor in 1971, and when it happened in my Acro Sport a few years back it took a while for the fog in my brain clear and check that the primer was locked--it wasn't then, either. Both surprising as the primer gets almost no use here.
Surprisingly that possibility revealed itself again, but no, the O-200 in the Emeraude doesn't have a priming system.

[Steve Pierce]

the Emeraude doesn't have a priming system.
Flew a CAP10 some years ago quite a bit, what a sweet flying airplane.

[59pacer]

Flew a CAP10 some years ago quite a bit, what a sweet flying airplane.

The CAP must have inherited the Emeraude's handling. I fly the Emeraude for it's wonderful handling, the Acro II for some 'yank and bank', and the Pacer for going places. Lucky for some!!

[Steve Pierce]

I flew the factory CAP10C into Oshkosh one year for the factory and the controller called me an Emeraude. I remember thinking "this guy knows his airplanes". Through some contacts I had at the FAA I was able to get the C model (carbon spar carry through) added to the Type Certificate Data Sheet.

[59pacer]

I removed the air box to get access to the Venturi(2 piece). It wasn't loose. I could then get better access to the idle mixture screw and found it was over 2 turns out when the manual says it is normally about 3/4 to 1 turn out. As the idle jets are at the rear of the carb, I imagine that it would be feasible for the rear cylinders to run quite rich. After putting it all back together and doing the idle mixture/ idle RPM adjustment tango, the idle is set up perfectly with the screw about 1 turn out. Run up is now normal, and after a short 10 min flight the carbon fouling on the #2 upper plug was almost nonexistent. I'll do another longer flight in the morning and pull the plugs again, but I suspect the issue is resolved.
Thanks for the input.

[59pacer]

I flew the factory CAP10C into Oshkosh one year for the factory and the controller called me an Emeraude. I remember thinking "this guy knows his airplanes". Through some contacts I had at the FAA I was able to get the C model (carbon spar carry through) added to the Type Certificate Data Sheet.

There was always some doubt in my mind as to what model my Emeraude was. It first flew in '64 and there have been various model numbers attached to it from the official CASA registry down through various owners. I found someone at the registry in Canberra who was able to access the original airworthiness paperwork in Sydney and that revealed that the original plans showed Piel Emeraude 100, so the registry has been corrected--as have my personal details on the forum.