I got the mower up and running yesterday and I just started with the blades. I was going down a hill, that i have done the past few years. It sounded like I ran something over but I didnt see anything and then my mower died. It won't start but it goes chug chug chug then sounds like the engine scrapss... New spark plug, oil filer, air filter... Any advice, I tried to look at the blades nothing seems to be holding the blades back.. Thanks for your time.