My nearly new RV-12 had 17 hrs when I purchased it, now about 80 hrs. The oil turns black very soon after each annual change. My A & P does not find any mechanical reason for this, but finds the spark plugs and exhaust tailpipe very black with soot indicating an over rich mixture. The engine performance appears normal, no apparent oil consumption, fuel burn 4-5 gpm. Is this problem normally associated with heavy carb floats without any other symptoms? Another RV-12 owner believes it is a problem caused by excessive vibration in the gearbox, but I don't see the correlation. Anyone have black oil problems without other symptoms? Is it really just heavy floats? Thanks for any advice.
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