There are two things that commonly cause kickback on the starting system. One is overly advanced ignition timing, and the other is lack of rotational inertia in the engine. So, for example, a sheared flywheel key can cause the ignition timing to be anything at all, and trying to start an engine without the flywheel or blade plate attached can cause lack of rotational inertia.
If you try to start your slasher without the belt drive to the cutting disk, or with the cutting disk removed or the driving belt slack, you will get exactly what you got.
