I picked up a Scotts 20hp/50" garden tractor w/ a briggs & straton for $600 about a moth ago, well the more I use it the slower it gets.. when I got it reverse was really slow and forward was what it is now. I tried to manipulate the linkage to get more out of it but that didn't work, so what I did was bend a piece of metal that was under the foot peddle that didn't allow me to push the reverse side of the peddle down far enough, it worked, but I know something's wrong. any suggestions?