Originally Posted by the smudger
This might help.
Twin spark was designed to clean up emissions. If the o2 sensor sees a rise in HC's (Hydrocarbons, unburnt fuel) the Engine control unit fires the secondary, up to 60 degrees ATDC.
An easy test is to let the bike idle, disconnect the secondary coil (the lower one) on each side one at a time. If the engine stalls then the problem is the Primary coil on that side.
They fail quite regularly but are difficult to pick up on because if the primary fails, the o2 sensor see's a raise in HC's, then fires off the secondary. It is quite usual for a primary coil to fail and the rider be completely unaware until its ridden hard.
When ridden fast (high engine speed) usually a misfire or 'holding back' is experienced. This is because the engine is spinning so fast that the engine controller cannot fire the secondary quickly enough to counter the failed primary.
There, that makes sense doesn't it.....
While I don't disagree with you, I do think this sounds like a Mickey-Mouse way to fire an engine, especially if the primary ignition system is junk to begin with.