Mine was not the timing or squish, it was getting past a stubborn stage..
Found that it was much easier to kickstart than pull start, and it got much easier the more hours i put on it !!
I remember now ..
Only prime the bulb so the fuel only just reaches the carb it use to flood very easy which would cause it to lock out and kick back..
Tip the motor to one side and be gentle on the primer bulb, pretty sure this was the main cause of the problem…
How many hours have you on it have you checked the needle and membranes i replaced mine after about thirty hours !!