[RIF]

Pull the cord until you rotate the piston until TDC and where the crank suddenly rotates with less resistance. Let the cord recoil and give it your best yank.

Any engine will kickback if the crankshaft is turning slowly enough when the spark fires and it can't make it over TDC before burning is underway.

This is why it occurs for you only randomly, it is because you are doing the above albeit unknowingly starting in whatever position it last stopped in.

PS when you shut an engine down pull the cord until the tension is on the valve. If long term storing squirt a small amount of 2 cycle down the spark plug hole (even if 4 cycle). Also I spray a long blast of carb cleaner in ALL my carberated engines from time to time, from the lawnmower to the motorcycle.