I have a Cub Cadet, push mower, model 11A-18MCO56, with a 1P70MO engine that pull starts, extremely hard. It will pull the recoil starter cord right out of my hand. It has finally broken the plastic starter parts on top of the engine. Before this happened, I checked the valve adjustments. They appeared to be ok. I have not removed the spark plug & cranked the engine. I will do that today. Has any one had a similar problem ?