Has the tractor just basically sat over the winter and ran good in fall? My first place to look would be for water/ rust in the carb bowl. there could be other issues too. Let us know what you find.

I see this is a continuation of another post. It is helpful if a) you post the pertinent info in one place, b) you respond to posters that give advice. If you choose to ignore them then what is the point of posting on a public forum? Engine model #s are helpful. They are probably stamped on the valve cover. If it seems to be running mainly on 1 cylinder, then the 2 most likely possibilities are either a valve issue or in some cases one side of the carb's fuel pipes or jet is clogged. Good luck.