Hi, I don't know your engine but it is common to have two ignition charge coils under the flywheel - a low speed one and a high speed one. Their characteristics are different and one takes over from the other automatically as the engine is revved - the output of one falls as the other rises. The ignition charge coils pump up a capacitor, which is inside the CDI unit, to a voltage of approx 200-300v. This current is released through the primary winding of the ignition coils and again increased in the secondary winding to a value suitable for arcing across the sparkplug electrodes.
I guess, if your motor has this system, that one of the low speed charge coils could have failed.