Hi everyone, first post. I have access to 3 John Deere 525’s. One of them works great and is fast (engine speed and ground speed). The other two have slow engine and ground speeds. I can’t seem to figure out how to increase the engine speed without major surgery. Am I missing something simple. Engine hours between 500 and 1000, normal maintenance as far as I know. The slow engine speed equates to slow ground speed and time wasted (custom mowing). These mowers work great otherwise. Starting is somewhat poor (need lots of choke), but are great for trimming around trees, etc. Any help would be appreciated. Thanks, Kid