Hi Norm and Tyler, I have had this kick back problem on a few mowers,as long as the blade is not slipping on the crank boss and the boss is not slipping on the crankshaft and the flywheel key has not sheared.
I would check the air gap on the coil to flywheel,by increasing the gap the timing is retarded.
When mowers have too much advance they kick back.
I've increased the air gap on a few mowers with this problem and it's worked to stop kick back.
I've also found a light bar blade doesn't cut as well as a heavier blade plate ,I have added weight to a light bar blade and in my opinion the mower cut a lot better and did not stall in long grass.
A boss cut in half then added to the crank should be enough to notice a difference you can also use a half inch piece of flat steel between the boss and the bar blade,the engine would need spacing up 1/2 an inch to compensate , this adding of weight needs to be professionally done for safety and durability reasons .
