i was out friday and motor feels rough on idle, on plane it feel a litte sluggish ...

but i dont think so much of it , cruising at 4000 rpm and POW !!! rpm get up to 5300 and speed 60 mph.... and i dont have moved the trottle ??? i couldn't stop it was rough sea ... when i check later a plug wire have comes off , and i see some corrision in plug wire.... after i cleaned it upp an remount the wire , it still feels sluggish w/ some vibration so i wonder if the coil broke when i run it w/ spark-cap off ??