Since it is a hydrostatic drive, the oil in the left pump may be contaminated. Try putting new oil in the left hydro pump. It should take normal 20w50 motor oil in the hydro. I don;t know exactly how these country clippers are set up but that sounds like it may be the problem. Hydro transmissions tend to run real crappy when they have really old or contaminated oil. I hope that helps.
-brandon