I have a Toro Groundmaster 120 with Koler twin V the engine doesn't seem to revup as high

When I go to full throttle it seems to be not as high as it has been in the past. When I turn on the blades it doesn't come up to speed full speed and boggs down.  I have changed the fuel and plugs and oil filter and oil and also the fuel.
When i push on the lever where that spring connects to in the one picture the engine revs up. Something maybe governor .
Anyone have any ideas what is wrong.?????????????????
 
Hope some one can help me.