One cruddy plug...

[Tim Holt <holtt@nacse.org>]

My '74 MG Midget seems to have one spark plug that consistently gets 
gunky.  The car progressively gets rougher, I pull that one plug, and 
it's black and wet.  Replace it, and all is well, for a while.

So.  I'm guessing it could be intermittent spark, or it could be 
something funky with that particular quarter of the engine.  What does 
the group mind suggest as a good plan of diagnostics?

PS
Is this list moderated?  IE does someone approve all posts?