There is a chance that the timing is now "off" on the engine since the blade hit stone. Pull and check the condition of the spark plug, If it is black and sooty and the engine ran well before, the flywheel key may have sheared . This isn't the end of the world but a little bit of mechanical skill will be required to check the key's condition and/or replace it. Typically when the blade strikes a very hard or fixed object, this is what happens. A little aluminum key breaks instead of the engine!