I started this project back in 2011 & took a long time to find a suitable transistor that would work reliably switching the coil. Eventualy found the 2SD1071 fited the bill. But was shuting down after a few minutes running due to switching spikes. This was cured by fitting a Mosorb 15KE200A (1N6303A). It runs fine on my old 2stroke lawn mower,