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.....
Your comments that the primary and secondary plugs fire at different times is interesting. I haven't read this idea elsewhere and haven't seen signs that it happens in the GS-911 data that I've been collecting. I'm not disagreeing but would like some more info. Here is some spark data I took last month.
While I can believe that the Motronic might somehow use the O2 measurements to affect spark timing on the secondary plugs, I've seen no signs of that and haven't read elsewhere that it happens like you say. And on a technical note, the O2 sensor has no ability to measure unburned hydrocarbons. The O2 sensor's output voltage stays near 800 mV until it senses oxygen in the exhaust (lean mixture) at which time the voltage drops to about 100 mV. It stays at 100 mV until the oxygen is gone (stoic or richer). It is only an oxygen sensor not a hydrocarbon sensor.