Sounds like you do not have the governor/throttle linkage hooked up correctly. If you look in the Kohler engine manual, which you must have since you rebuilt the engine, in section 6 there is a spec on how to set the governor arm properly with no load on it. Figure 6-47 shows you the correct linkage assembly and how to do the initial adjustment on the governor. There is nothing in the engine or governor that provides the spring back. Then there is a spring that goes from the lower governor arm, to a small plate with multiple holes in it, where the throttle hooks up. Then the adjustable linkage goes from the top of the governor arm to the throttle on the carburetor.