After having flown over 160 Hobbs hours during the past 14 months (90% on ethanol mo gas), my RV-12 ELSA exhaust outlets also exhibit a light, black sooty coating on the inside of the pipes. Everything about my engine is running great, spark plugs are normal, etc. I understand that such a sooty coating is normal for 912s and reflects the effects of idling without a traditional mixture control. Sounds normal to me.
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David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 940+ hours (as of September 2020)! 
V AF donation through June 2021.
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