john deere Lx 255 15 hp kohler...what would cause this mower to stop running at just about any time and then after i wait at least an hour or so it will start right up...deck can be ingaged or not...new plug installed .basic tune up just done ..takes me an hour and a half to mow my lawn and it;s not a good feeling not knowing if i'll get to mow it all or have to wait...any ideas?...thanks in advance