Burnout the transistor is a problem from using the flightbacksystem.
Normaly the ocsilator will stopped if the HV is 2 or 300 Volt.
At low speed this Voltgae will there be sooner then when the engine is running fast.
The transistor will be shorted for a long time at low speed.
A CDI don't use this, he must be open untill the capacitor is loaded, not longer.
I want to try the schematic below if my brain is working back OK.