especially the cap, the crack(s) hold dirt and stuff which tends to be conductive. The crack becomes a path to bleed off some or all of the spark to ground resulting in weak or no spark at the plug.

Just to update my escapades, I put the front back on on Sunday (with the secondary vaccuum passage blocked till I get the new diaphram), and fired the car up, but it ran horrible. I left the thing before I put a wrench through something expensive. I went back to it last night took a look and noticed the brake booster hose still disconnected. I optimistically hooked it back up. Cranked it and it fired up strong and smooth even considering my monkeyed settings!
It seems way fast on the idle but thats better than falling through the floor. While in the garage, I looked at one of my boxes of old BMW parts and spotted the dual barrels of an old Sole poking out of one. I picked it up and lo and behold, it also has a vaccuum actuated secondary. I took it apart, and the diaphram is a match for the Zenith....except for the threaded hole, it has an M4 I need an M3. But I have JB Weld (a metalized two part epoxy) so I mixed some up, filled the hole and left it to dry. Tonight I'll drill it out and retap it, I have M3's here at work. I'll let you know how it goes.

Mark