I find this transformer in a old computer-powersource.
I use also normal scotch-tape, I don't dip the coil jet.....first it have to work properly (thats now)
The spark is great and powerful with the coil I use, it's a coil from a mopped (50cc).
(I putt a pic on the site, so you can see what I mean)
Remove the iron from this coil and solder a lead on it (=ground)
Only still one problem......I get a high Voltage back from the ignition to my power-source.
I think I need a other diode in the + from the battery to eliminate this.
I"ve still one question about using a R-C (22nF/400V and 22 Ohm) on the + - from the diode-bridge.
See [link=http://www.transmic.net/dccdi/dc-cdiFLPS.pdf]R/C[/link]

If you like boats, [link=http://www.modelbouw.gompy.net/wild_thing/wild.htm]Wild_Thing[/link]
This one is ready now [link=http://www.modelbouw.gompy.net/wild2/index.htm]ild_Thing 2[/link] and I will use the ignition on this boat to perform the speed to more then ~70 Mph.
I have to wait the ice is melt and the weather is better, very cold this moment (0 degrease in daytime)

BTW, my name is Rob