Once again back to square one. As advised, I took carb apart, and soaked it, cleaned all passages and jets good , made sure all was clear, used Dremel tool and polished inside good removing all trace of oxidization, let soak somemore, cleaned jets again, put together with all new gaskets. Put 100% gas in it along with some atf as suggested. Started up and ran perfect. Drove it around, and killed it and restarted about a dozen times, ran great. Today mowing, it ran perfect and mowed fine for about an hour, then surging badly once again. I have had it, it is in oklahoma just south of tulsa, and going to be for sale cheap. It is a 520H with 800 hours, 48" deck, forward swept axle. I am done with it!