Sounds to me like theres some gunk in the carb that clogs up the idle jet now and then. With 250,000, its definently time for a rebuild.

If you don't have time right now, you could try my little 15min rebuild trick. Take the top of the carb off to expose the float bowl. Use the little straw attachment on your carb cleaner and spray out each jet. Clean out any grit in the bottom of the float bowl. Put the top back on and I betcha that'll help out at least until you can do the full rebuild. Its worked for me a few times.

Good luck,

Scerb

http://www.scerbfab.com/carb_faq.html