I change the schematic a bit, the oscillator will start by himself (=spark) and don't stop.
You can find some pic on [link=http://www.modelbouw.gompy.net/cdi/]CDI[/link]
I use a transformer like Charlie do, but you must place some paper between the two ferrits.
I place a diode between the cathode and anode and some 100nF caperistors in the power line.
It's important to feed the boards from the powerboard to the pic-board and not otherwise.
C7=4,7uF/16V, if you use a other SCR, you need to resize the resistor R6.
You need more current to open the gate, for example BT148=200uA / TIC126=20mA !!
Change R9 = 10kOhm and use D1=1N4007