I have a 36" Toro wb belt drive with a 13hp and a 52" wb with a 14hp. Both are Kohlers. There is a significant difference in power between them. The 52" has a very noticeable drop in rpm when I go from varing lengths of grass, whereas the 36" doesn't hesitate for a moment. Does the extra blade add that much load? Even when I have the sulky on the 36" it is still stonger than the 52". The rpm's on the 52" do recover but they really drop first, almost like the speed governor or carb is not right. Any constructive ideas? By the way other than that the 52" with the 14hp runs perfect and uses no oil, runs clean as could be.