Phil;
Interesting, my Honda 600's normally don't run at all on a fouled plug. But I have noticed that the electrode cap for the spark plug wire can be the cause. The wire catch on the inside of the cap bends or breaks off causing the connection to be loose. Or, I didn't thread the end into the wire tight enough, again causing a poor connection. I made a note in my log to watch for it the next time.
Thanks
Bill