I have been following this thread and I think I may have a suggestion that has not been mentioned yet and has not been considered. I just spent time trying to get a ULS on a Kit Fox to run smooth again. Long story, but. Take a close look at the choke ( enricher lever ) action when opening it and closing it. Make sure the travel is same for each unit especially to be sure both enricher go completely closed. If one was letting fuel flow, it would probably put the carbs out of balance and not run smooth. If both were allowing fuel to flow equally then you would have a smooth running engine, with extra fuel being introduced inside the air filter where you see the fuel stains. Is this extra fuel and leak seem to be occurring on both filters or only one?
After a thorough investigation I have found the cause of the yellow fuel stains on the engine cowl and on the fuels trays.
It is the fuel that I buy regularly from a Total Erg station since two years. The stains showed up two years ago but I did not pay to much attention as I could not detect any engine misbehaviour.
Only recently I decided to start the investigation which concetrated on the carburetors of course. These where in operation for 16 year (1450 working hours). After they failed the needle valve (viton tip) test I decided to replace it with new ones.
These where tuned in all aspects and operated perfectly but the stains did not disappear.
I checked positively differential compression and absolute compression.
I perfomed borescope observations of the cylinders finding the heads of the pistons rather "encrusted".
I even reinstalled the original muffler that I had replaced at 600 hours with a stainless steel one but with different internals ducts (by the way it was working well for 800 hours before the stains appeared).
Finally I emptied my fuel tanks filling that with 100 octane automobile fuel like Shell VPower (I do not know if you have it in the US).
After two flight of about one hour each I found everything dry and no stains anywhere.
The flights where performed in conditions equal to those for which stains appeared.
Therefore from now on I will change the fuel station where I buy the fuel for my plane.
Roger I tested also the engine and prop cruise settings you indicated. Let me tell you that I am not too much convinced.
At 5000 ft. driving the pitch to get 5800, WOT and then throttling bach to 5200-5300 leaving the pitch unchanged I loose from 10 to 15 km/h which means from 5 to 7 knots less on my cruise speed which usually is 100 kn (indicated) at that altitude.
I fly a Tecnam P92, 80 HP.
Maybe the engine is less stressed and maybe the fuel consumption reduces (to be checked) with your settings but now it is a matter of personal preferences.
Thanks
Sebastiano
Glad you found your problem.
5800 rpm is too flat. You have a good climb prop, but a bad cruise prop. Set the prop pitch to get 5600-5650 rpm at WOT for 5000 rpm.
5800 rpm and throttling back will do exactly what you describe. You will loose cruise speed and fuel economy.
Roger Lee LSRM-A & Rotax Instructor & Rotax IRC Tucson, AZ Ryan Airfield (KRYN) 520-349-7056 Cell
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