Did you note the color of the plugs? Mine was recently running too rich giving black plugs and irratic running as well. Leaned it out a little on the carb and it runs much better, in my case anyway. A little oil on some plugs may mean leaky valve seals as well, especially if you get a nice big puff of blue smoke on start up after it sits a while from the oil seeping in down from the heads. I am no technical expert, but it is what I saw in an pretty descriptive auto engine text book recently.
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