I wrote a lengthy reply to this thread yesterday, but I guess I screwed up somehow and it didn't get posted.
erubin is right. You can't use a general purpose oscope on the secondary side of the engine.
In the days of point ignitions, the ignition scope was very necessary. Now with the flame thrower ignitions and 100,000 mile spark plug life, these things are either in the junkyard, or like mine, is in the corner gathering dust. and being used for storage.
You could obtain or fabricate a high voltage probe to step down the 50KV or higher secondary ignition voltage to be viewed on a general purpose scope, but I feel that this would be a waste of time. The occasion for the need of an ignition scope these days is EXTREMELY rare.
Hope this helps,