Are you sure the govenor linkage is tight on the shaft? And do is it adjusted properly, I had one that wasn't properly adjsuted that wanted to take off, re adjusting per the manual made a huge improvement in the engines desire to want to over rev. Wasn't so lucky with another one. One last thing to check not that it won't keep you from a rebuild but might change the parts you are after. Loosen the linkage and try to rotate the shaft a full 360 degrees, if you can the stop attatached to the shaft has come loose / broken and you will need to replace that. The gears are available new from any Kohler dealer and shaft should be also. Don't skimp on the gov. repairs as they are a pain to get in and work on.