a long shot but make sure the connection at the coil is clean and tight. I drove myself crazy replacing coils periodically before I finally discovered the real problem was the female connectors from the wiring harness. A clue is if there is any evidence of arcing on the blades of the coil. Knock wood, bike has run great ever since (shite, no wood around, will my head do? now I've done it!).
Good luck and let us know.
_________________
-Jim
'93 MC21