Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I'd be  a bit careful to ensure that if you are pulling off the HT lead and testing the spark, that you make sure to earth the spark plug outer part so when the ignition discharges the energy can go to ground. I blew up my ignition unit be messing with the spark plug out of the engine and turning the crankshaft. I believe  that the energy from the HT can arc across inside the unit if the HT circuit has no earth return. This is a known cause of failure in full size CDI ignition units too.

I had to use Jan Ridders ideas to make a new ignition unit ( see my ignition thread here) and since I did, I have taken care to avoid the problem happening again.

I have experimented with spark timing and find it runs fine just around TDC. Mine is set very slightly before TDC at the moment, but it tends to kick back when starting unless given a strong flick.