Make sure the starter has a clean ground. Most Kohlers are case grounded on the starter, if material or corrosion gets between the starter and the block you can end up with a situation where the starter just doesn't turn as well as it should.
If that checks out fine I would pull the valve cover off and turn over the engine by hand to make sure the compression release is engaging properly.
Briggs and Stratton Master Service Tech
Kohler Expert Tech
Echo / Shindaiwa Tech
Char's Small Engine