Lesson learned when I was 16, and re-learned this weekend - always look for
something stupid. First off, I found the adjusting thread on the SU jet
bearing scored, preventing me from leaning out the mixture. Then, the jet
linkage was not fully returning to its top (lean) position, caused by choke
cable misadjustment. Lots of black crap out the exhaust, and, finally
black / dark slate colored oil. Borrowed (now bought) a Colortune with the
jet bearing kit, and it showed the mixture rich throughout the rev range
(duh). Changed the oil, fixed the carb, and thoroughly cleaned the left
side of the engine to find the side cover is leaking, which was what was
causing runoff down the block and eventually onto the exhaust pipe. A
jury-rigged tin cup and safety wire assembly tied to the draft tube outlet
after stopping showed only a few drops of discharge after a long drive
today. There was enough overflow from the engine flooding previously to
cause a more alarming amount. My "it's a big deal" meter is currently at
40%, down from 95%, and will hopefully be lower this weekend after sealing
up the side cover. Good oil pressure and compression have been comforting
all along.
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