What's wrong ? (Was:MMC partial failure)

Hi All,
         after my last post I headed straight for the garage and ran the coil 
flat out for 1/2 hour with the secondary shorted and the gap as wide as it
go to see if the cap would fail from over voltage but the darn thing just 
won't blow.  I checked all the caps afterwards for warming but they weren't 
even slightly warm.  
It is nice to know that my system will run for 1/2 hour without anything 
melting, exploding or breaking down, but as the pulsed arc problem persists I 
would still like to get to the bottom of this.

Perplexed in GB
Nick Field