Have hade my Sport Zero Turn for about 4 yrs now with no problems. Change the oil and sharpen the blades each spring. Have begun having stater problems where I'll have to turn the key multiple times to engage the starter. Recently the mower will hesitate, pop and sputter. Any ideas where to start looking? I have searched for an engine manual and haven't found one, yet. I'll keep looking. In the Mean time I believe the first thing is to change the spark plugs, and it looks like the drive belt is loose.. so I'll order a replacement. Are there any other possible things that could be causing the hesitation? Thanks.