I need help adjusting the linkage on my YT6800. The mower is running at what sounds like excess RPMs. The mower boggs down on slight inclines and heavier grass. The engine doesn't compensate for the heavier load. I have tried to adjust the linkage but can't seem to get it right. This problem began when we tried to adjust the linkage to compensate for dirty air filter (couldn't find filters at the time). Can anybody give me advice on how to get back to the correct set up? Dink