It's a 1-jug 16hp verticle shaft on a Wheelhorse. Blew white smoke twice, sputtered and then kept running normal. Now chokes black smoke and fouling the plug. A mechanic said something about a seal accessible from the bottom, so I pulled the engine and saw no sign of leaking on the shaft seal, and the oil pump/filter O-ring looks good.
Any ideas? I've good compression and the carb appears to work fine. This came on suddenly.