Join Date: Jul 2009
Location: Olds Alberta
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The black could be just a fuel/combustion issue with other causes but your best diagnostic for what you are wondering about is to have a HOT compression test done and also a leakdown test done - both tests done on both cylinders.
Once that is done then you know what mechanical foundation you have to work with and you can move on to other possible causes if required.
Also, a recheck on the valve clearances would be in order - even the best can have a slip of the wrench... and the "sewing machine sound'' is not a reliable measure of an accurate valve adjustment.
Then again, a clear picture of both plugs would be helpful. it may be closer to normal than you think....
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