I am not sure if you can get just the needle valve only, you may have to get the entire rebuild kit and that would be the wiser thing to do. You will have to know what carb. is on your machine. There should be a metal tag on the carb with the carb. number...usually they end up missing. <!-- s:roll: --><img src="{SMILIES_PATH}/icon_rolleyes.gif" alt=":roll:" title="Rolling Eyes" /><!-- s:roll: -->  Most dealers are really helpful with the ID of the carb if the # is gone.  If that gets too frustrating, at least take it apart and clean everything out good, it may have been a small piece of dirt holding the needle valve open.
   Korves or Maibach will have the parts, or your local AGCO dealer

KORVES-    1-618-939-6681
MAIBACH-  1-800-808-9934

                        Cal