I have a 3 year old 36" Exmark with a 13 hp kohler. I'm wondering when it's at full throttle if it's actually at full throttle. I can move the lever slightly into the choke position and the engine will have higher rpms without choking. But if I take it much farther it will choke. None of my other equipment does this sort of thing so I was wondering if the throttle cable might be streched. If so, are they easy to change?