Try bypassing the ignition switch wiring with a jumper from battery voltage (battery + or the big charge lead of the alternator) to the coil + terminal and check for spark that way. You can get correct "voltage" but insufficient current flow through a dirty switch connection, loose wire, etc.
By far the most common cause of insufficient spark is a set of dirty or burned points. Remove them, and inspect them closely under a bright light. It's very likely you'll find something other than a clean, low resistance contact area. Try checking the voltage between the (-) coil terminal and a good ground with the ignition switch on and the points closed. If you get more than a couple of tenths of a volt indicated on the voltmeter, change the points.
Jerry
