Hi Norm,
I've had a lot of mowers that had the kick back problem on starting ,the shear key on the flywheel is designed
to break when the bar blade hits an unforeseen obstacle so the crank is not damaged .
It would be easy just to bolt one extra bar blade onto the Sprinter and see if the extra weight helps.
I would try a heavier blade plate if all else failed to fix the kick back problem,old coils can give a weak
spark and cause backfiring and old spark plugs can cause backfiring.
Cheers
Max
