Electronic Spark Generator Circuit

There is a spark generator circuit attached to every petrol engine on the planet, so what can you learn from them?

That schematic doesn't say which XGen Ultra Power transformer they're using for T1 and little info about much of anything.

That design also wastes half of each oscillator cycle.

How much current is being drawn from that battery. Is it one of the NiCd packs they're selling?

Either that transformer can't handle the current or the insulation is burning through. Can't handle the output voltage and breaks down.

In addition to europium's comments:

What are you using for the 9v power supply? Are you using a bench supply?

I don't see any current limit in the input leads to the T1 transformer, so the only current limit is the winding resistance.

I trust you read these notes from the website:

"This site does not advocate the use of stun guns.

Stun guns can be illegal in certain countries so check the law where ever you are.

We accept no liability for the misuse of this sites content.

When designing it is important to remember that stun guns are not toys and can inflict a variety of damage.

When designing please be extremely careful when working with high voltages and currents."

And note that the term 'when designing' is out of place; it should read 'when testing and using'.

http://xrsdesignsystems.com/page48.html

The web site is blocked from my work domain because it contains "Adult" material. Still, I can tell you this. A spark is loaded with high frequency components that can burn out a transformer. It is likely that what you need to do is to allow "some" of high frequency components and provide a bypass capacitor (in parallel with the transformer) selected so as to solve this problem. A series inductor could also be helpful in limiting how much high frequency component makes it into the transformer. This being said, there will be a range that works and a lot of values that have other detrimental effects on the circuit. We are basically talking about filter technology so that the transformer will be undamaged. Good luck and be safe! Keep it legal, because it isn't worth the consequences if it is not.